If you're not going forever, don't worry about it, just keep filing Canadian tax returns - if you're keeping a home, bank accounts, car etc.
If you're going lock, stock and barrel, then yeah, much more complex - but generally you're right, it counts as having sold them on the day you become officially non-resident. 'Tis a bugger. And it is all assets - your primary residence is tax free of course (but if you don't sell it you'll have to *start* paying tax on it as a rental or dispose of it somehow).
Bloody tax people cost a fortune though. I'm pretty sure it is possible to work through it, but yeah, even paying a couple of grand you might well be better off :-/