If you are doing some sightseeing head up Cadaliac mountain in Acadia National Park.  There are several outfitters that can help with any arrangements you might need.  Bar Harbor is OK, but a tourist destination, sea kayaking in the bay would be another fun excursion.  And whale watching would be another idea, they guarantee seeing whales.  
It sounds like the others had some good canoing ideas, so I thought some other things for a family to do.

btw, if you go to Bangor up that way, there is a restaurant/micro brew pub called Sea Dog, breat beer sampler, and excellent food.  Blueberry beer is a speciality.