1. Only if s/he is from a US visitor visa waiver country or has a US visitor visa. Visa waiver countries http://www.consular.canada.usembassy.gov/visa_waiver.asp
Mmmmm..... Study visa does not authorize re-entry to Canada, so you need to get Canadian Visitors Visa and you need to have visitors visa from the US as well i guess unless you are from Germany or any other country citizens of which can go to the US without any visas.
Mmmmm..... Study visa does not authorize re-entry to Canada, so you need to get Canadian Visitors Visa and you need to have visitors visa from the US as well i guess unless you are from Germany or any other country citizens of which can go to the US without any visas.