The question about leaving a boat gets asked quite a bit, and it's a good question. At all these river mouths you will be entering a cove where the river pours into the lake. The trail at each is a gravel road leading into the woods. Despite the wilderness setting, there is a good deal of human activity at these sites, with Hazel being the busiest. Hazel usually will have a park Ranger boat and/ or car stationed at the landing area. The others have park campsites at or near the lake.
You will likely have some company at the trailhead. There may be several canoes and/ or motorboats moored there. There is plenty of room to tie up or pull your boat onto the bank. Most of the boats are not locked, and I have not heard of problems or experienced any problems with theft. However, you are in a public area. If you are concerned, it would be easy to pull your canoe up the bank and chain or lock it to a tree. Keep in mind you need to leave the gravel landing area and gravel pathway open for the use of the park service's landing-craft style boat, that docks at these sites and discharges vehicles and other equipment, as well as the ferry boats shuttling passengers.