Leaf season isn't generally until mid-october. Mid-late September is really one of the best times to visit, weather wise. June can be fantastic as well but it tends to be the peak of the mosquito/blackfly overlap.

Depending on what kind of outdoor activities you're looking at doing, July and August tend to have pretty similar temperature ranges and risk of fire hazard. If you want to kick it by the campfire, the earlier in July the better while we still have some rain left over from June. If you're looking to stay outside all day enjoy some hiking, the end of August is sometimes starting to cool down into our beautiful September weather.

If you have the flexibility in your schedule, June or September tend to be much nicer months to visit.