Is there any chance of being refused entry if I'm visiting Canada for the purpose of marrying my fiancée?
She wants to stay in Canada at least until January 2014 to satisfy the requirements for citizenship, so I'm planning to either get a study permit right after we marry, or attend school onlne and just leave and re-enter Canada every six months.
You can certainly try to extend your stay by applying extension. If you have enough fund, going to school is not a bad idea. It will give you "Canadian educational experience" and peace of mind if you are thinking about immigrating to Canada. Just you will have to bare international student fees, which is very costly.