Google Canadian Doctor Salaries and you'll find a listing of FP and specialist salaries. Its a bit province specific, but seemed to be about the same as US salarie averages but in C$ so at current exchange its 25% lower salaries....but you're not dealing with malpractice insurance bills like the US and its a single payer system (ie the guvment) so its simpler for you to deal with paperwork, not a different deal for every patient.
Basically it comes down to if you like nationalized health care or not. My experience with it has been great, but I've only experienced it in rural areas. Docs in Canada have a nice salary but some are jealous of US doc salaries. Some who have moved to the US are returning now because after malpractice insurance they are making less than they were. But it ain't any easier to get in to school, probably harder (fewer spots for the population), and really hard as an international applicant. And no you can't go back and forth easy to practice. Being nationalized its burocratic licensing hell.