The previous suggestion about planning around the seasons is very important. You are talking some very different climates on this trip! It is kind of like planning a hike on the Appalachian trail to start in the warmer south and work north as the weather gets warmer or reverse. I'd also consider doing it in two trips - because there really are two different great big loops - basically east of the Mississippi and west of the Mississippi.
When you are at Acadia – that should just be the start of your northern journey. On the border you pass a great historic site – the only American National Park on Canadian soil – Roosevelt's Campobello compound. Really a wonderful FDR and family experience – and not too many folks go there.
What people like about the Maine coast – is even better going north through New Brunswick and Nova Scotia. The Canadian coast is ideal for Rving. Don't miss the tidal bore in the Bay of Fundy... and Ft. Louisburg, an amazing historical site – the only “European” city built in North America that doesn't have a modern city built over it... north of Halifax. If you like lobster... lobster every day from fresh catches, also amazing giant scallops. Prince Edward Island is a whole different experience. Quebec – like going to a little French city – though don't try to take your RV into the really old city where the old streets still exist - we had trouble with a van!
Montreal is a great metropolitan city with both history and art.
Back down through the other sites mentioned... Niagara Falls, the Great River Road along the Mississippi, etc...
So... the East makes a great several month loop all on its own.
No time to go into the West loop... lots of favorites there, too!
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