Boston to Nova Scotia and back, 7 days, what not to miss

I was there for a few weeks last summer. Off the top of my head I'd recommend:
Cabot Trail (Cape Breton Island) (Not to be missed. Exquisite drive.)
Camp Breton Highlands National Park
Peggy's Cove
Bay of Fundy
Chocolate River (astounding!)

Please note that the Welcome Centers are great; some will even make reservations for you on the spot!
There are also markers throughout for self guided tours, i.e. lighthouses, covered bridges, etc.

With or without an itinerary I'm pretty positive you will enjoy Nova Scotia!