This is a fine example of American cluelessness when it comes to legal immigration into this country. Telling someone to "just get a green card" is quite hilarious. How exactly should he do that, hmm? Any suggestions aside from marriage?
This person is right in stating, however, that you will need to do some talking and convincing, but if IMGs can do it so can you.
You do have numerous advantages (like first year of residency as an OPT, nobody will question your qualifications, etc.) -- that being said, the best advice I can give at this point is to just focus on school for the first two years. You'll have plenty of time to consider your options.
If you insist on looking into it now, I recommend you search for terms such as "Canadians in US medical schools" -- there are a lot of Canadian internationals in the States and they like to congregate to talk about their options. Whatever applies to them will most likely apply to you as well.