If you are planning a land trip in that area, I highly recommend the Cabot Trail in Nova Scotia. We took a small group private tour on our Sydney stop. We could only do part of the trail due to time constraints, but the scenery was incredible - especially in the fall. We've been to a lot of beautiful places over the years, but this was special. We definitely plan on returning by car and driving the entire trail. The other highlights for us were Quebec City (basically a trip to Europe without having to cross the pond) and Acadia National Park in Maine. Everyone should see the view from the top of Cadillac Mountain at some point in their life!
We were on NCL for our second cruise to the area and it went to a lot more places than
DCL did. I think if DCL really wanted to give that area another shot, they need to add ports and maybe length (ours was a 12 night cruise).