I haven't been to New Brunswick (other than through it) - but if you're into paleontology, the Joggins fossil cliffs are supposed to be neat. The Bay of Fundy for both, of course - see a tidal bore if you can. In apple blossom time (especially), the Annapolis Valley is pretty. On the other shore, Lunenberg (home of the Bluenose II) is worth a visit. Cape Breton Island is probably too far for one day, but well worth its own visit - Louisbourg, in particular, is a must-see. In Halifax, enjoy the waterfront, and go see the Citadel (just a few blocks from the water). about 8 years ago
Visit the Hopewell Rocks on the Bay of Fundy. The tide comes in and out every 12 hours, so depending on what time you are there, you can walk along the beach and see these magnificent flower-pot-shaped rocks or if the tide is out, you can canoe along the shore.
Drive throuh the Bay of Fundy National Park; it's stunning.
St. Andrews-By-The-Sea in New Brunswick near the Maine border is a charming little town to visit and is home to the landmark Fairmont Algonquin Hotel. You can take whale-watching tours (highly recommended) from St. Andrews-By-The-Sea into the Bay of Fundy where you'll see other wildlife such as puffins and American Bald Eagles. about 8 years ago