I'm sure that happens, just as foreign trained doctors are
hired by American Hospitals, including Canadians, though they don't stand out. I just have no statistical evidence, and failing that, I'm disinclined to make a judgement. We just don't know how rife the system is with this sort of short circuiting of the system, but at least students who return to the US are US trained.
If you want meaningful change, insist that medical schools take more qualified American applicants until the shortfall is over, there's no shortage of qualified applicants. The same thing is true here. We have foreign trained doctors, but the Ontario Medical Association (the Doctor's Union) has an iron grip on Medical School enrolements in Ontario, and keeps the tap turned on to trickle. Why? Because doctors are then in short supply, and therefore are in a stronger position when bargaining with the Province over fees and reimbursement. In this case it is not Universal Healthcare or insufficient funding that is to blame, it is the Doctor's Union.