Got it. I answered this question in a different thread previously, so I'm copying and pasting my answer from there.
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You will likely need to apply through VSAS. That's the Visiting Student Application Service. Most institutions in the US use this system to apply to away electives. There are a few exceptions where the institution will have their own custom application but these are generally the more selective hospitals e.g. Harvard. In fairness, I doubt that the more selective programs which aren't on VSAS will accept foreign applicants anyway.
Looking at VSAS now, there are several EM programs which take international students.
University of cincinnati
Wake forest
Florida hospital - orlando
Akron Childrens
University of new mexico
University of Rochester
Michigan State U
Maricopa integrated health
George washington U
SUNY downstate
I'd guess that there are more beyond that, but I don't know for sure. It is hard for international students to get into US programs though. I've done EM rotations at 3 different hospitals. At two of them there were international students, however, they were all observers and were not allowed to see patients in the role of an intern, so I don't really know that I'd call that an "elective" so much as "prolonged shadowing time."
EDIT: the two places that I worked at where there were international observers were NOT on the list I posted above. In other words, I'm guessing the list above actually will let you do an elective, whereas hospitals not on the list might let you stand around and watch.
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I don't have any information for you about electives in Canada.
And to reiterate what I wrote in that previous post, the list above only includes programs which are on VSAS and accept intl applicants. My suggestion for finding out (besides internet sleuthing) would be to ask your dean.
I would also suggest looking at the thread I originally posted in as there was some information about other programs (the EEC) listed there. Here's the link:
http://forums.studentdoctor.net/threads/foreign-medical-students-and-emergency-medicine-electives.1035542/
Bon chance.