Well the only part of the East coast that I know really well is Nova Scotia.
I live on the main land, but the highlands up around Inganish are always beautiful. The roads are a bit wavy, and their are a fair amount of sharp turns because for alot of the trip you are going up mountains, but it makes for a fullfilling ride. The main land on the other hand is relatively flat, lots of highways and stuff. not as nice as the highlands though.
Ah, they all sound really great, I can't wait to get out there.
But don't forget that the Cape Breton Highlands are worth seeing too.
I mean they are really nice and would make for an interesting drive