Let me give my 2 cents from a Canadian perspective. We recently moved to Nova Scotia, and last fall the colours were brilliant right to the end of October.
If you're stopping in Halifax, make sure you visit the kiosk on the pier selling Beaver Tails - a delectable treat!
You also don't want to miss the Maritime Museum, also located on the pier, which has an amazing exhibit if you are at all interested in the Titanic.
Don't know if the cruise line offers harbour tours, but you can probably get one while in port. You can sail on a big ship, or just a harbour ferry for some beautiful views of the upscale homes and local colour.
Hope you enjoy your cruise - the Caribbean Princess is a favourite of mine!