Welcome to the RTA Forum!

10 days should be plenty of time to make the trip. You could do it in 4-5 days if you pushed it, so you'll have more than enough time to do some exploring along the way.

There are hundreds of different route possibilities, but there really is no standard "best" route. The ideal route for you will depend upon what sort of things you are looking for and places you'd like to see.

One bit of warning, you'll likely want to do some research about your car rental situation. I'm not sure if you'll be able to find a company that will rent you a car in Canada and drop it off in the US. You may have to find a way to Buffalo and pick up a car there.