I planned to travel to canada. Currently I am holding F-1 visa. I have asked the IES in my university about if I need a valid visa (my current visa is expired) to enter into canada and come back. They said as far as I got their signiture on my I-20, and take some other documents, I can go to canada and come back without a new visa. I really need to make sure the information is correct. Have anybody been travel to canada without a valid visa? thanks for sharing your information.