Travel for Canadian Citizens
Canadian citizens do not require an entry visa to enter the U.S. from Canada, but do require an I-20 (F visa) or DS-2019 (J visa). All Canadian citizens are required to show a passport to enter the United States.
Those entering the U.S. to study should request F-1 status at the border and must show the Form I-20 or Form DS-2019 and supporting financial documentation to the immigration officer at the port of entry.
Be sure to check your I-94 (paper and electronic) to make sure that the I-94 was properly noted with F-1, D/S or J-1 D/S.
If you have a paper I-94, often, it will not be removed from your passport when you leave the U.S., and you will not receive a new one when you re-enter. This is not a problem. Just be aware that if the I-94 card is removed, you must get a new one (or receive an electronic I-94) with the F-1 D/S notation when you re-enter.