回复：急问加拿大登陆回美及签证

You don't need a valid visa to return, but you need to have endorsement from your school.

If you apply visa from Canada as a new immigrant, you may get:
1): multiple entries based on valid date of your I-20;
or 2): can not return to US if your visa was denied.
Most likely, 1) will be the result.

Good luck.