Halifax: We did the harbor walk, Maritime museum, Keith's brewery and the public gardens which were beautiful. There are a lot of shops in town and neat things to see along the way for both kids and adults.
St. John: I had booked a kayak trip with an outside excursion provider who was told by the port people that our ship wasn't coming in so he left. I think they try to keep outside people away, so you may want to be careful when booking outside excursions. I had booked a whale kayaking trip, which was not an excursion the ship offered. After finding out the bad news, we ended up paying a taxi $50 a person to take us around for 4.5 hours. We saw the caves, a lighthouse, almost got ran over by a moose, the reversing falls, historic downtown and ate really good fish and chips at the caves. The town is pretty small, it's much nicer if you go out and see the natural scenery.