This took me a while to find, so I thought that I'd post the link so that nobody else has to waste time slogging through the Revenue Canada website.
In short, if you fill out this form and are a non-resident, it means not paying tax on your earnings in Korea. I think. I'm a bit muddled over the whole thing - a lot has to do with your primary and secondary ties to Canada. I don't have a house, car, dependent children etc in Canada, but I do have a bank account, passport.
I don't know if this is mandatory or not... I mean, really... if I were better with money, I wouldn't be in Korea to pay off my debts in the first place, right?
http://www.cra-arc.gc.ca/E/pbg/tf/nr73/README.html
