Originally Posted by MoreMilesPlease

Remember that you need to tell the rental car company if you plan to take the car into Canada. Many won't let you or will charge an extra fee. I have had the Canadian Border agents ask about our car before and it was my own car.

If you have already bought airline tickets for specific dates see what the change fees are. You may not have much airfare left or the fees to change will be more than the tickets.