We are sailing on the Maasdam round trip out of Boston in August.
I visited the Maritimes on the Star Princess in Oct 2006, and particularly enjoyed the "Reversing Tides" excursion in St John, New Brunswick. It is a ride on a small boat during the time when the tide is swirling in the Bay of Fundy and it was a lot of fun - prepare to get wet, although protective outerware is provided. Unfortunately, we will not be able to experience it this time, as the tide conditions will not be right.
Make sure to walk through the market in St John - well worth the time to see the local wares (the fruit wines were delicious!)
The view from Cadillac Mountain is spectacular - we had a crystal clear fall day at the summit.