Janan and I have paddled on all sides of Mt. Desert Island many times and it is awesome. While Bar Harbor itself isn't bad (The Porcupine Islands), we find we prefer all the other "quieter" clusters of islands to the south and west (The Cranberrys, Baker, The Gotts, Black, Placentia, and Bartlett).
Any of these can get strenuous with wind, current, and chop, and yet, at the right time (slack water, no wind) they can be perfectly easy and calm.
Haven't seen any Puffins. We see the most seals by Dawes ledge (Black Island), and Harbour Porpoises often cruise between Little Gott and Black.
Baker has beautiful wild roses on it. Low tide exposes zillions of colorful starfish dangling from the west banks of Placentia.
At slack water we had a nice paddle North from Pretty Marsh through the Bartlett Narrows and saw a bunch of porpoises there, but another year made slow progress thru the Narrows as they can develop a pretty strong current.
We have seen several bald eagles in Sommes Sound. Even this area, while protected from the open ocean, can develop quite a strong wind and chop.
There are several outfitters in downtown Bar Harbor who can perhaps suggest a good destination based on the days' weather conditions.
Have a great time.