For TheConservator:
The Canadian political scene was pretty static from the 50s till the late 80s, with the never-winning NDP on the left, the usually-winning Liberals in the center, and the occasionally-winning Progressive Conservatives on the right.
Things changed when the Progressive Conservatives were decimated in the late 1980s under unpopular Brian Mulroney. In Quebec, former Mulroney cabinet minister Lucienne Bouchard split and formed the separatist Bloc Quebecios. In the West, the right wing fled the Progressive Conservatives for Preston Manning's new Reform Party. Thus the coalition Mulroney had constructed to win two of the largest majorities in Canadian history collapsed: The party went from 169 Members of Parliament to 2 Members of Parliament in its first election against Jean Chretien.
The right wing remained divided all through the 90s between the Progressive Conservatives and the Reform Party. Realizing the electoral cost of being divided in a first-past-the-post system, the two parties tried a couple of times to get together, but mutual suspicions kept foiling the process. (There were still many Progressive Conservatives from the Mulroney years high in that party, and, after all, the Reform Party was founded in opposition to precisely those people.) The Reform Party was the first to bend, changing its name to the Canadian Alliance and inviting the Tories along; under the leadership of "Red Tory" Joe Clark, however, the Tories still weren't interested, and the Canadian Alliance (formerly the Reform Party) remained an alliance of one.
With Joe Clark's departure, the last hurdle was cleared, and the Canadian Alliance merged with the Progressive Conservatives to form the new Conservative Party. Thus it stands today.
Fairly simple, to sum it up: Start with three parties, the NDP, the Liberals, and the Progressive Conservatives. Then, in the late 80s, two new parties form: The Bloc Quebecios and the Reform Party. After a decade, the Reform Party (now called the Canadian Alliance) and the Progressive Conservatives join up to form the Conservative Party.
It'll be interesting to see whether they get anywhere in this election. The Conservatives have a relationship with Quebec something like that which the Democrats have with the South; they can't win the country without stealing that region. John ("Dief the Chief") Diefenbaker and Mulroney both built solid Quebec bases, and it won them elections, just as Johnson, Carter and Clinton were able to parlay Southern support into Democratic presidencies. But with a separatist party now consistently winning most Quebec seats, making Quebec somewhat un-stealable by either major party, it'll be interesting to see what happens. (Imagine, if you will, the effect that the ensconcing of a Southern separatist party that pushed out the Democrats and Republicans would have on American politics.)
The Canadian Left now faces a situation exactly the mirror image of the one the Right faced in 1993: its vote is divided among three separate parties that don't like each other much to begin with and pursue different agendas. This is where it helps the Right, now that conservatives have unified under a single party.
But by Australian standards the Liberal Party (Canada) corresponds to the Left of the Australian Labor Party (ALP). None of the past two ALP Prime Ministers are leftists (Bob Hawke and even Paul Keating are both pro-American). On the right the Liberal Party and National Party are either as right or even more conservative than the Canadian Conservative Party.
On the side Australians consider as political fever swamp aka the Left of ALP, they have the Australian Democratic Party and Green Party. Both are equivalent to Canada's New Democratic Party and are nutty left-wing by Australian standards. Australians largely shun these two parties - they get around 4-5% of the vote. None of these two have never reached outright majorities alone st state level (the best result the Greens and Democrats could get is at the most left-wing Australian state Tasmania. But even there they could only get around 18% of vote)
I wonder what makes Canada's politics far to the left of Australia, let alone the United States's?