Definately the Cabot trail on Cape Breton is a must see. Some prefer to travel the trail clockwise, others counter clockwise. If you are nervous of heights, I'd suggest you do it clockwise, that way you are not driving close to the edge. Be prepared for some fairly steep grades. While you are on Cape Breton, a trip to the historic Fort Louisbourg is well worth the journey. The city of Halifax attracts a lot of people, there are many points of interest there. From Halifax continue down the south shore to Peggy's Cove. Peggy's Cove is a beautiful fishing village that has been painted by artists from all over the world. Try to arrive somewhat early in the morning to really appreciate the beauty and tranquility of the village. If you venture onto the rocks by the lighthouse, be wary of rogue waves. Each year someone gets too close and gets swept into the sea. A little further down the south shore will bring you to Lunnenburg, home of the Bluenose. Here you can visit the fisheries museum, go whale watching and take a tour of the Bluenose if she's at home. From here you could continue down the south shore to Yarmouth and then to Digby where you could hop on a ferry to St John, New Brunswick or Bar Harbor, Maine.
These are just a few suggestions. Nova Scotia is a beautiful province and there are many, many things to see and do. Enjoy your trip.