First off, Quebec, nor any other province should have the right to break up the country. Since it seems they would be permitted to do so under certain conditions, they should be forced to take with them their share of the debt, be given no special trade or diplomatic treatment not given other separate nations, and be given none of the benefits and privileges of being part of Canada. If you want to leave, off you go. Completely and totally.
That being said, if it happened....it would be the end of Canada. The Atlantic provinces, cut off from the rest of Canada, would probably have to join the US, as they wouldn't be viable as a nation unto themselves. (although I don't believe there is anything in the US Constitution automatically granting statehood to Canadian provinces)
The West and Ontario might hang on longer, but the pyschological blow of the country's initial breakup might convince the rest of the provinces that end is inevitable, and they need to get and keep as much for their own selves as they can before it all comes crashing down. This would lead to disputes over things like transfer payments and political power, further breaking down national unity into a sort of regional identity.
The US, seeing this chaos, might well believe the end is nigh for Canada, and believe the time has come for a largely united North American nation, to combat a rising China and EU. Discreet diplomatic signals might be sent, informing the remnant of Canada that it would be warmly welcomed into the Union, should it choose to do so. After much debate, the provinces of Alberta, BC, and Ontario decide that the economic and political advantages are too great to ignore, as well as the stability such a move bring. Saskatchewan, Manitoba, and the territories being too weak to exist as a nation themselves, would have no choice but to be swept along. An agreement would then be hammered out, bringing in those provinces as states, with a few changes, as PEI likely wouldn't qualify for statehood by itself.
Quebec, being surrounded on all sides, having little bargaining power, and dealing with an indifferent, uncompromising Washington, instead of an accomodating, eager-to-please Ottawa, would stubbornly carry on for a few years, until finally, deeply in debt and on the verge of collapse, it becomes the last former province to become part of the United States. No longer a sovereign nation. No longer having its whims catered to by a cowed federal government. No longer even being able to whisper of separation.
There's your outcome for Quebec separation. Kind of a sobering thought for the Quebec separatists, huh?
