Becoming a doctor in Canada...Watch
First off you need to do an undergraduate degree before applying to medical school. Even if you did your undergraduate degree in Canada, without Canadian citizenship you are limited to maybe about 20 spots in the whole country for internationals in medicine(believe me they are unbelievably competitive). To apply for residency training, you still need to be a Canadian citizen, so all in all, its a nearly impossible endeavor.
Its easier to just do all your training in the UK and then decide if you want to move. That way, if you decide not to move you can practice in the UK. If by that time you do want to move, Canada will welcome you with open arms.