would like to know the best route from toronto to orlando?

Dukecdn:
see if your library has an old copy of Along the I75. It used to have a profile of the route so you could see the elevation and get an idea of the length of the grades.
The significant grades that come to mind are Tennessee and climbing out of Cincinatti southbound, short but steep.
Last time we were at Harbortown the washrooms were open. (several years ago)
Do not expect water or sewer north of Kentucky; possibly not north of Tennessee depending on weather.