The US and Canada are two different countries so being allowed to work in the US has absolutely no significance for Canada. If you want to work in Canada, you need a work permit. If you were studying in Canada and wanted to do an internship, you would apply here:
http://www.cic.gc.ca/english/study/work-coop.asp but since you are not studying in Canada, I don't know. Maybe just a regular work permit.