You can, but expect the airline to refuse to board you (personal experience, several times). Airlines are on the hook if you are refused entry into Canada when you arrive, so if you don't have a return ticket they can recover the cost from, they have to pay the return trip. Be prepared to buy a return ticket at the airport if you try.
Edit: It's also a pretty good reason for CBSA to refuse you entry into Canada. Lack of intention to leave Canada.
