Not at all. There are several US trained physicians working in my hospital. But that doesn't mean it's really easy, particularly if you want to work in a "desirable" area. Even in my rather run-of-the-mill hospital in Eastern Canada, lately the number of US applicants for the posted attending spots has sky-rocketed. (Maybe because they're afraid of what will happen under Obama-care? I don't know.)
The first step (whether you trained in Canada or the US) is to have your training recognized by Royal College. See this
link - it gives all the info and the necessary forms, etc. Once your training has been assessed, you then are eligible to sit the Royal College Exam.
Once you have passed your Royal College exams, you can seek license to practice medicine from the province that you're interested in. Most provinces require you to also have the MCCQE Part I and II exams (these are sort of like the USMLEs). By way of example, this is
Alberta's process for seeking licensure in that province. You need to contact the province that you're interested in for the details.
So, it's not that you can't come back and practice. But be aware that - at least at my end of the country - there have been an increasing number of applicants for a limited number of positions.
Long story short: if you want to practice in Canada, do residency in Canada (if you can). If you want to practice in the US, do residency in the US.
If you're going to be a US trained
family doctor, see
here. Because the country is much more desperate for FPs than for specialists - and particularly if you're willing to work in rural/remote areas - the licensing is much less stringent.
I have no idea, sorry. But try reading this
link - I think that this group of people may have helpful suggestions.
