Newport is a tender port and we took our time getting off the ship since we didn't have a shore excursion planned. We walked about 2 blocks to the Visitors Center and bought tickets for a trolley tour for about half the price of a similar tour available from NCL. We didn't tour any of the mansions but we drove past several of them on the tour. It's easy to see Newport on your own.
Quebec City is my favorite port of the ones on this cruise. We explored on our own this time having taken a tour on our last visit. We found a great restaurant, le Continental, a few blocks from Chateau Frontenac and had a wonderful lunch. Everything is just a short walk from where the ship docks. Again, the visitors center has tours available if you haven't prearranged anything.
We were only in Sydney, Nova Scotia for 5 hours on this trip and didn't get off the ship. There's a large craft market at the pier but you really need to get out of Sydney. If we had more time we would have taken one of the shore excursions but we didn't want to feel rushed.