We found the municipal campground in Saint John, NB, to be a pit. You know there' going to be trouble when a boil water order is posted on a billboard driving in. Mind you, this was a few years back, but I'll never try it again.
Prince Edward Island: Marco Polo Land. Sounds hokey but it's a great CG. Big sites and all grassy. Again, a few years ago.
Nova Scotia: seeing the Fundy Tides are a real must. You can actually see the tide coming in. Alexander Graham Bell summered on Bra d'Or Lake and did some great (and early) research into hydrofoil boats. There's a very good museum of his work there, with many of the boats.
Also, the fort at Louisberg-- an important battle in American history. Very interactive -- any kids will love it.
fred.