If you use a service like Rent-A Wreck (they aren't wrecks) and get a passenger van, that might help. Or renting from a regular car place mid week is cheaper.

Call Budget or National rent-a-car, locally and on toll-free, to ask about age restrictions in ON.

Another possibility - don't rely on bus tours, as such - check out good old Greyhound! Your hotel might have some information for you as well.