As a native New-Brunswicker, I think you can't go wrong spending time in either NB or NS. There is a lot of diversity of coastline along these two provinces, and traveling along the east coast of NB into NS would allow you to see a lot of it.
One place that gets overlooked sometimes is the Bay of Fundy. Fundy National Park near Alma is gorgeous and has a lot of beautiful coastline views, but further up the road is the Hopewell Rocks where you can walk out to the rocks at low tide. Low tide also offers the chance to photograph boats sitting on the bottom of the ocean!
St. Andrews is, as mentioned, very picturesque and you have the chance to visit some of the surrounding islands (Grand Manan, Deer Isle, Campobello). Whale watching is also very popular.
Cape Breton is fabulous, but it is a ways to go to get there and the Island itself is pretty big so getting to the northern most part of it from the Canso Causeway is a couple of hours of driving.
Hope you have a great trip!