We did 18 days staring from Washington DC and driving up the eastern seaboard as far as Boston, taking in Philadelphia, New York etc on the way.
Then we went west to Buffalo before turning back to Niagra Falls and crossing into Canada. Spent a night at Lake Elizabeth (in the same Hotel as the about-to-be-elected Canadian Premier, Jean Chretien) before moving on to Toronto.
From there we continued west to Sarnia where we hooked up for a few days with some old friends who had emigrated there, before crossing back into the US and going to Detroit to see all the US Automaker HQs, the mansions, and the Henry Ford Museum at Dearborne which is highly recommended.

Dead easy to drive around over there: road speeds are relatively low, and the traffic flows much better - perhaps because you can overtake on either side so most folks keep their wits about them!

Just be aware that car hire isn't as cheap as it is in Florida, and you need to make sure the rental company allows you to take their car across state lines.

Still want to go and see some of the West coast, so let us all know how you get on.