If you are from a visa exempt country like South Korea, you don't need a travel visa to enter Canada so you should be fine. Somebody who is from a country where they normally would need a visa to visit Canada would still need a temporary resident visa to enter. Work permit only allows them to stay, not to enter. If you know anybody like that, tell them to apply for a multiple entry visa at
http://www.cic.gc.ca/english/information/applications/visa.asp And always if you want to make sure, call immigration and ask.