Well, I certainly hope that they are better at doctoring than they are at driving. Unless the goal is to build up a huge number of injuries with their cabs, then be allowed to practise medicine to clear the backlog.
Seriously, the cab-driving-doctor has become a cliche. Has anyone here ever personally met such an individual? One who is fully qualified to practise but is held back only because of his/her immigrant status? Because I just spent the day at a Toronto hospital undergoing tests and every single person I dealt with was from somewhere else - Poland, Asia, India, Carribean - and every single one of them was exceedingly competent and professional. So I have trouble believing that the medical system in Ontario is actively blocking qualified people from working.
I'm the son (and brother) of immigrants, so I know a little of what people face when they arrive, especially 60 years ago. But one thing my parents did that no longer seems popular is they lined up jobs in their respective professions before they got here.