Well, actually, there is no problem with, for exmaple, marrying a citizen
There is. By marrying a citizen or PR you express 'immigration intent' (remember the question on the non-immigrant visa application). While this doesn't automatically exclude you from re-entering on a J1 visa, it may.
I presume that means well known to the US government, yes?
Yes, the US goverment (as represented by DOS and USCIS).
What about the Canadian government, do you think it knowingly participates in this?
Yes, by issuing 'letters of need' during the duration of the visa and by failing to enforce the return of service contracts.
Other countries whose goverments don't want their physicians to leave via the J1 visa route just don't provide the 'letter of need' (Israel for example used to be very reluctant about sponsoring physicians to go to the US).
No. But it is the just desserts the Canadian government gets for their poor planning and unfair and unjust treatment of otherwise suitably trained professionals.
One disconnect here is between the canadian goverment on one side, and the provincial physicians colleges and the RCPSC on the other hand. The goverment (mostly at the provinical level) tries to come up with all kinds of programs to increase the supply of physicians, the RCPSC and the provincial registration boards try to sabotage each one of them.
But in general, I agree that they get what they deserve. If they weren't such a@@%% about recognizing US qualifications (and would fix some problems in their physician reimbursement structure), the net leakage of canadian docs to the US would be far lower.
(btw. I am not canadian, and the country I come from is very aware of the J1 system. Our constitution specifically provides for ones freedom to choose where to live and work. As a result, the goverment provides me with administrative and consular support if I choose not to live and work at home.)