Jackie,
We love this area and itinerary.
Halifax: You should look into the tour that takes you to Peggy's Cove. A cute little village and lighthouse with a great story. I won't tell you the story, you should go. Leave time to explore the city also. The Wharf area is fantastic, some great shops and restaurants.
St Johns: You must do the reversing falls, there are so many excursions for this. It's wild to see how the tide changes from morning to night.
Bar Harbor: Take the bus tour to Cadillac Mountain. When we reached the top the ships in the harbor looked like toys floating in a bathtub, you are really up there.
Boston: They have a fantastic Aquarium across from the Market Square. The Market Square is worth a visit.
That's the extent of our visits to those places.
Just a little note, We love the Halifax area. We can't wait to return, we actually thought of moving there in the near future.
Hope this helps.