I keep saying this: bringing down the government on one particular issue doesn’t mean that it will be the only issue talked about for a 6 week election campaign.
That is a crucial argument to remember, when people wonder about the logic of forcing an election over immigration reform. The Liberals have already framed their stance as accumulative, the "markers" approach, which I think easily translates into a campaign. Yes, by bringing down the government on immigration, you effectively make it a central talking point, it is the catalyst, but it doesn't mean a campaign revolves around this one issue.
First off, the government is more likely to want their campaign to revolve around their supposed "achievements". I suspect the main lines of attack will revolve around leadership, a concerted effort to paint Dion as fiscally irresponsible. In other words, I don't see how a protracted debate over immigration plays to the Conservatives preferred arguments. Hebert mentions Quebec, but I don't see how the Liberals are mortally wounded, given their remaining base, in fact it could shore up things, or at least make it all a wash.
If the Liberals take down the government over immigration, I think it will be rightly framed as the final straw, a tipping point in ending this long minority reign. Couple that fact, with a Liberal Party platform finally released, which is sure to hold a few surprises, some bold measures, and immigration is probably on the back burner by the end of the first week.
If Dion is serious about a carbon tax, then the environment will rear it's head as the defining issue. The idea is fresh in the minds of British Columbians, Quebecers are largely on board, it will make for an interesting debate in Ontario, and the Conservatives will rally their base, who are strongly opposed. In other words, the environment will become the lightning rod, a combination of voter interest, regional considerations, stark contrast, not to mention all the parties willing to engage. If the Liberals release their environmental platform during the election, an issue like immigration will fall off the radar, but it will have served it's purpose, demonstrating to certain groups that the Liberal tradition remains.
In Ontario, you already have Liberal buttons, which say "My Canada Includes Ontario", does anyone doubt that the provincial Liberals and the federal party won't do everything in their power to make Flaherty, the economy, manufacturing, working together, a central thesis in a campaign? Does anyone seriously think we will all be consumed with the immigration reforms?
I just don't see an environment where the country is plunged into a debate on immigration, at least not in a way that dominates this campaign. I also don't buy into the idea that voters would "punish" anyone for forcing an election, after all this minority already has historic distinction for longevity. So long as the Liberals properly characterize their vote against, as more the absence of proper consultation, hiding these changes in a suspicious way, I don't see the negative fallout. A vote against is a matter of principle, woven within the greater theme that the Liberals have decided it's time for an election, based on a host of considerations. I suspect the media will accept that rationale, because after all they have been consumed with election speculation for months, waiting on any trigger.
An election campaign is very organic, there are bound to be twists nobody can predict. To base apprehension for an election on the premise that immigration isn't "the" issue for the Liberals to bring them down seems to rely on unnecessary tunnel vision. With all the points of distinction, a platform everyone has desperately wanted to see, a government less than inclined to fight on this ground exclusively, other issues which continually show themselves as important in the public consciousness, I think the trigger, in this case, is mostly secondary.