visa to 回美國 and visa to Canada

Your immigrant visa for Canada will be cancelled once you land in Canada, and the Maple card is supposed to replace that which will allow you to enter Canada freely.

Even as a PR of canada, you still need a visa to come to the US. But if you only leave US for Canada for under 30 days, you can't still return to the US without applying for another valid US entry visa. In order to take advantage of the 30 day rule, you havce to take your I-20(signed), passport and has a valid I-94.