Ok, here's what I would say. Try to rent a canoe trailer from the place your renting the canoes. Or, rent a flat trailer from a rental center.
If you can not do that than here is one last option: Make sure the rental cars, vans, or trucks your renting have a factory roof rack. Then bring pair of six foot 2x4's, and straps to attach those to the factory rack. Instant cross bars. Strap on canoes and go. If you don't want to take the boards with you, just stop by a hardware store after you pick up the rental cars.
I love to dance, but who needs the music- It throws me off.