The Australian model is interesting, because it merges an American-style Senate with what is fundamentally a Westminster parliamentary system. Here are some choice quotes from the Wikipedia entry:

The Constitution [Commonwealth of Australia Constitution Act of 1900] intended to give small rural states added voice in a Federal legislature, while also providing for the revising role of an upper house in the Westminster system.

Although the Prime Minister answers to, and must serve as a member of the House of Representatives (the "lower house"), other ministers may come from either house and the two houses have almost equal legislative power. As with most upper chambers in bicameral parliaments, it cannot introduce Appropriation Bills (bills that authorise government expenditure of public revenue) or impose taxation, that role being reserved for the lower chamber.

In practice, however, most legislation (except for "Private Member's Bills") in the Australian Parliament is initiated by the Government, which has control over the lower house. It is then passed to the Senate, which may amend the bill or refuse to pass it. In the majority of cases, voting takes place along party lines (see also: conscience vote).

There are detailed conventions and rules regarding situations in which the Senate and the House of Representatives disagree. If the Senate repeatedly refuses to pass legislation initiated in the lower house, the Government may either abandon the bill, continue to revise it, or call a double dissolution (election for both houses of Parliament) and attempt to pass the bill at a subsequent joint sitting of the two houses.

The constitutional text denies the Senate the power to originate appropriation bills, in deference to the conventions of the classical Westminister system, under which the executive government is responsible for its use of public funds to the lower house, which has the power to bring down a government by blocking its access to Supply - ie. revenue appropriated through taxation. The arrangement as expressed in the Australian constitution, however, still leaves the Senate with the power to reject or amend supply bills or defer their passage - undoubtedly one of the Senate's most contentious and most powerful abilities.

As a body intended to provide greater representation to smaller states, the Senate (like many upper houses) is necessarily relatively unrepresentative; Tasmania, with a population of 450,000, elects the same number of Senators as New South Wales, which has a population of 6 million. Paul Keating called it an "unrepresentative swill". But the proportional election system within each state ensures that Senate incorporates much more political diversity than the lower house, which is basically a two party body. Consequently, the Senate frequently functions as a house of review, intended not to match party political strength in the lower chamber but to bring in different people, in terms of geography, age and interests, who can contribute in a less politicised manner to the process of legislative enactment.

In 1975, there was a crisis in which Prime Minister Gough Whitlam had the support of the lower house, while the upper house refused to pass supply bills. The action instigated by an opposition that had more members in the Senate than in the House of Representatives, and who hoped to force an election. Whitlam refused to resign, but the government had no access to money, which is a non-confidence situation. But then he did have the confidence of the lower house. The conundrum was resolved only when Governor-General Sir John Kerr dismissed Whitlam's government and appointed a caretaker government on condition that elections for both houses of parliament be held. Australians still debate today whether Sir John did the right thing, and whether the Senate should have the power to block supply bills.

To follow the Australian model, we would allocate Senate seats to each province. In a purely American model, each province would get exactly the same number of Senators. I can't see any government in Quebec accepting that situation, sensitive as they are to having their power diluted, even if by increasing the power of a smaller province such as Prince Edward Island.

In fact, the fight over the form of a new Senate will be the most contentious one of all. Anything that offends Quebec's sensibilities with regards to what it perceives as its rightful allocation of power will never pass in the province, and become grist for the separatist mill.

So do we give every province the same number of Senators, or do we tell PEI that it will have to continue to share power with the other Atlantic provinces? How about Alberta? Alberta shares the western allotment of Senators with British Columbia, Manitoba, and Saskatchewan. How many Albertans believe that as a province, they deserve at least as much representation as Quebec, considering how much Albertan money flows into la belle province? But bring up that issue in those terms, and the fireworks begin.

I should be fair and point out the Ontario stands to lose power under the same conditions, but Ontario has traditionally not been as defensive about power-sharing, and in any case, there is no Ontario separatist party standing in the wings ready to use a new Senate arrangement as a way of winning a referendum on sovereignty.

Is a by-province approach the only model for a Senate? Not necessarily. The point of the upper house is that it is less representative than the lower house -- it can make decisions based on factors other than majority will. Some countries reserve seats for "constituents" such as trade unions or the military. Should we have one or more Senate seats for the Senators representing Canadian women? Selected how and by whom? Will pro-life women be as welcome as pro-choice? How about an equal number of seats for representatives of the male gender, or is that assumed to be true by default? Is that a fair assumption? Will women's groups give up their special seats as soon as women are elected in roughly equal numbers to men?

Is the military a constituency? Maybe in some South American countries, but probably not here. How about trade unions? Which ones? Do academics get a union seat along with auto workers? How about a seat for non-unionized workers? What happens when they vote against the union workers on bills that affect the use of non-union labour during strikes?

Seats for the Senators representing Francophones? But then don't they already have the Bloc Quebecois in the House of Commons? All Francophones, or just the ones in Quebec? And what about Anglophones? And Allophones? Would Quebec tolerate a bloc of seats for other languages that could be counted on to nullify votes from the Francophone Senators on language issues?

Do First Nations people get special Senate seats? If so, what other cultural groups? Descendents of the original British Loyalists? Pur et dur French representatives too? Immigrants?

Muslims vs Christians vs Jews? Oy vey!

Do homosexuals constitute a constuency? If so, do heterosexuals?

Who selects these special constituency representatives? Obviously not the general population. But where do you draw the line? Are fundamentalist Islamic women allowed to voted for Muslim Senators but not for Women's Senators, since their attitude to women's issues are unlike Judy Rebick's?

The American and Australian model of the melting pot eliminates this sort of debate, since in the view of their respective governments, all Americans and all Australians are the same. In Canada, however, we've institutionalized multiculturalism and feminism as government departments, creating legally recognized constituencies out of these groups and of others. Any reform of the Senate will have to tip toe around this potential land mine.

So we'll probably retain a geographically based model, but then what of Alberta and PEI? Will they tolerate a muted voice in a new upper chamber? And as soon as the Senate issue is opened up, I'll bet that someone, probably the First Nations, will demand special set-aside seats for non-geographical constituencies. But as soon as the First Nations demand it, you can bet some of the groups I've listed will realize that they can have a guaranteed voting block to push their agenda by demanding the same. Quebec will resist furiously (except on the issue of Francophone set-asides), while the others point to Quebec as having their own special interest party in the Bloc Quebecois.

It could turn into a real mess unless handled carefully.

The issue of whether to eliminate lifetime appointments in favour of a six-year election cycle will be the least important problem to solve.