As I recall there really aren't many private tour companies at these two places.
When I was there last year with Royal Caribbean we went to the tour desk at the pier and got the hop-on-hop-off tour bus and I think we paid either the same or more than if we'd bought it on the ship. This was a nice way to see Halifax.
Bar Harbor is a small town. The ship has to anchor there. We took the ship's tour to Acadia National Park and then had a leisurely lobster lunch in town. I don't think any of the major rental car agencies have a presence in town, and the little airport is not close.