Once you get through a residency, you'd probably have no more trouble landing a Canadian job than a Canadian grad.
Obviously, psych would pay better than FP.
Obviously, Montreal is way cheaper than Toronto (and, for most people's tastes, nicer).
FPs are needed in many places all over Canada-- mostly rural spots, of course. Some provincial governments will fork over big incentives to convince immigrant docs to practice an agreed-upon number of years in an underserved location. After that, you'd be free to move on, of course.
But yeah-- overall if you do a residency in the States you shouldn't have any particular problems finding a job or getting licensed in Canada. Your citizenship doesn't matter, really.
Sorry I don't know whether psychiatrists are in particular demand right now.
