James Bow's most recent post touches on the past 20 years of Canadian federal politics, and looks ahead another 10. It's one or two orders of magnitude better than what I've been writing on the subject, so I suggest you go read it.
Over the past decade, the opposition in Canada has primarily been on the right, while the NDP left has been relatively silent. During the same period, we've seen the federal Liberals shift rightward. This is partly because of the dynamic of the opposition parties, but they've also been pulled rightward by the comparison to the United States, and also by the realities of governing in the post-deficit era.
As James reads the current environment, it would seem that the Martin Liberals now own the centre-right of Red Toryism. This limits the chances for the new Conservatives, but presents a big opportunity for the NDP. If they are able to take advantage, we may see the Liberals pulled back to the middle.
What this brings to mind is a self-adjusting system, in which the Liberals attempt to effectively execute the central consensus in Canada. They form the government most of the time, but may lose power from time to time under the right coincidence of events and leaderships. However, all the major parties have a siginficant role to play as they struggle to reach out to Canadians and form the opinions that ultimately decide where the centre really is.
You can draw an analogy with the normal distribution curve. The centre portion is always home to the most of us. However, there's nothing to say that over time the mean can't be shifted one way or the other.
As citizens with points-of-view about what's best for Canada, our long-term goal isn't to ensure that any particular party wins. It's to convince enough Canadians of our point-of-view that the mean comes closer to it. This is actually what democracy's about -- debating with and convincing your fellow citizens, and then forming a government that reflects, as well as possible, this consensus.