"I would be very surprised if they voted against the budget," said a person close to Mr. Ignatieff. «Le gars [le premier ministre] s'est mis à terre, il a donné à peu près tout ce qu'on veut. "The guy [Prime Minister] went ashore, he gave almost anything you want. If we end up with 30 or 40 billion dollars in deficit, will we ask for more?"
There are two chief issues here that confront the Liberals, and both revolve around optics. The first is outlined in the above- how do the Liberals rationalize a vote against the budget, if said budget comes with many of their demands, if it represents a significant departure for the fiscal update? No reasonable interpretation expects the Conservative budget to completely mirror what the Liberals want. But, a partial overlap does give the Conservatives some room to argue that they've responded, they've tried for compromise in a minority parliament. As the above suggests, if we see a substantial deficit, with significant stimulus, infrastructure money, then any vote against risks looking too political for the Liberals. The public won't pour over the finer details, if the broad strokes show a Harper climb down from the past, there will be little appetite for quibbling.
Many people just assume, that if the budget is defeated, historical precedent will allow the coaltion to form. We all know the arguments, but I don't put much faith in believing that Jean will turn to the opposition. I don't think you can discount public opinion in any decision, the public want will surely be weighed. Even more important, don't discount Harper's ability to argue for an election. IF, Harper brings a budget that addresses some of the root demands, he can then make a case to Jean that his government has responded to this crisis, and the opposition's continued resistance speaks more to a want for power, than the idea of making parliament work. Look at where we were, look at where we've moved, clearly this isn't about good government. Harper will surely push this angle to justify another election, and one can easily see how Jean could support the logic. Stephen Harper is the only one who knows what Jean said during their meeting, and I suspect he is operating with that knowledge in mind.
Of course, all of the above falls apart, should Harper deliver another dud, or is provocative. Short of that, in terms of optics, the Liberals will be hard pressed to bring down the government, using any assumption on the coalition.