Lots to see and do along that trip and lots of really nice Provincial parks to stay at. Once you cross at Sarnia take hwy 402 east and exit hwy 21 northbound. It’s mostly a 2 lane road but follows the lakeshore north. Several parks just outside of great little towns to visit.
Here is the link to see the available provincial parks and reservations. The summer months you will have difficulty getting in. After September you should be fine during the week, weekends fill up fast still.
Grand Bend, Bayfield, Kincardine, Goderich, Southampton, and Sauble Beach are all great little beach towns with plenty of touristy things to see. From hwy 21 you have a choice of taking the ferry from Tobermory to Manitoulin Island ( shorter but $$) or going around to the east on hwy 26 to the 400 North.
The ferry route stay in Bruce national park. No hookups but a beautiful area. Checkout singing sands beach and the grotto. If going around, Awenda is a nice park to stay and see Marie Among the Hurons and Discovery Harbour.
Hwy 400 can every busy on weekends as it leads from Toronto into cottage country. It turns into hwy 69 amd then joins hwy 17 to the Sault. Several more nice provincial parks along the way. Our favourite is Grundy and the French River. A side trip a little out of the way to Sudbury for Science North museum and the nickel mine tour is worth it.
Let me know if you want more specifics.
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