The interior is highly unlikely to be "crazy busy" on Thanksgiving weekend as most canoeists won't go out that late in the season.   Personally, I would not make a reservation anytime after Labour Day weekend as the chances that the lake I want would be fully booked are low.   What does get "crazy busy" on Thanksgiving Weekend are all the day use hiking trails along Highway 60, and since so many people staying in the Huntsville area drive up for the day the traffic can be backed up quite far from the West gate.  We have experienced that traffic jam a couple of times while visiting friends in Huntsville.  Fortunately, we live in Ottawa so our more normal destination would be the north end of Algonquin.   Places like Lake Travers or Cedar Lake have hardly any canoeists on Thanksgiving weekend.