I've visited all of the Maritimes except Labrador, with many trips to New Brunswick, with most trips during July and August. Weather is usually on the cool side and often wet, depending on where you are. We have also has some amazingly beautiful weather-80s and dry. September can start to turn cool so if you don't like the heat, it's a great time to go. Climate is very similar to New England, as are the crowd patterns. Some campgrounds close as early as Labor Day weekend (or at least used to) but many are open until their Thanksgiving, which is our Columbus Day.
Places to go: Fundy National Park and Kouchibouguac NP in New Brunswick. Kouchibouguac is better in the summer as it has nice beaches. The Cabot Trail along Cape Breton Island in Nova Scotia is beautiful. Check out the Alexander Graham Bell museum in Baddock and gaze over the Bras d'Or Lakes. PEI has some of the most gorgeous beaches anywhere, Anne of Green Gables, and be sure to visit Charlottetown. Also, if you like Celtic music, a visit to the College of Piping and Celtic Performing Arts in Summerside. The two big National Parks in Newfoundland, Terra Nova and Gros Morne, offer some fantastic opportunities for hiking, biking, canoeing, kayaking, scenery, and wildlife. It's a bit of a hike and expense getting over there due to the ferry, but worth it.
