The stewardess rejected me departing from Canada to the U.S.?
Flight attendants are not immigration agents. They only have the ability to reject your boarding because you haven't followed airline policy. If your passport information does not match your ticket information, that would be a reason to be disallowed boarding. In your question you mentioned you printed your ticket as a Korean. If you used your Korean passport information when purchasing the ticket then tried to board the plane with your Canadian passport, you rightly would be refused boarding. Your ticket information did not match your passport information. Your name had nothing to do with this. It was incorrectly purchasing a ticket with one passport then attempting to board the plane with a different passport that was the problem.