What a beautiful cruising area this is! September should still be warm (I live in New York and I don't recall temperatures going below 70). But I recommend a few cotton sweatshirts or sweaters in case the weather cools down north of New York.
My post prized piece of clothing for this region: a water-proof poncho with a hood (no need for umbrella) and lots of pockets. You can never predict rain, especially in Canada.