Which border are you crossing?
If taking 95 (Houlton), make sure to stop in Fredericton.
1. If you like Art Galleries--Beaverbrook has some great works
2. Check out a play in officer square or take a tour with the Calithumpians
3. Take a walk along the river
4. Learn about the history by visiting Fredericton Region Museum in Officer Square
5. If there on Saturday, visit the farmer's market
If crossing at Calais
There are several interesting parks in Saint John (try Irving Nature Park) as well as Reversing Falls.
A must is Hopewell Rocks near Moncton, NB
If you want to camp, try Fundy National Park in Alma (close to Hopewell Rocks)
Alternatively, you can take the ferry from Saint John to Digby, NS
If you do that, you will want to check out the wineries in Annapolis Valley and the Lookoff
Camp at Blomindon Park
If you take the Ferry from Portland, ME to Yarmouth
You may want to stop in at Liverpool for the Hank Snow museum (if you are a country fan)
Then stop in at Lunnenberg, Mahone Bay, Chester (lots of beaches to visit in this area)
In Nova Scotia,
A must is the Cabot Trail and Ft. Louisbourg (both in Cape Breton)
Around Halifax,
1. Take in an outdoor play (Shakespeare by the Sea) at Point Pleasant Park (audio interpretive tour of park) (go in the evening to catch the sail boats)
2. Visit the Citadel in downtown and have a pint at one of the microbreweries and go for a walk and dinner/ice cream along the Harbourfront
3. If you are into music, see what is playing at the Carleton on Argyle
4. Take in a ghost/history walking tour (evening at Citadel)
5. If you are into the Titanic take in the Museum of the Atlantic or if you want to learn about Canadian Immigration (go to the Pier I Museum)
6. Eat at Chives (Halifax) and Seventy3 (in Dartmouth)
7. If camping, stay at Shubenacadie Park in Dartmouth
8. Take ferry to downtown Halifax from Dartmouth or vice versa
9. If on Saturday, take in the farmers market
10. Visit the famous Peggy's Cove lighthouse (stay away from black rocks). Keep going along south shore to Lunnenberg, Mahone Bay and have lunch or catch a show in Chester
11. Go to any sandy ocean beach (lots to choose from and watch the sunset or go surfing (Lawrencetown Beach)
12. If you like flowers, check out the public gardens.
13. It is the Natal Day long weekend, so check for events, including free concerts
PEI
If you still have time-- going from NS take the ferry
Visit Charlottetown and Cavendish Beach
Take bridge back to New Brunswick
That should keep you busy.
I would meet you for a beer in Halifax, but it is a long weekend, so will be out of town.