FWIW: We boondock/dry camp exclusively. On our 120 day trip end April to August 2019 (not one paid CG), we stayed at Espanola the night before crossing the bridge to Manitoulin Island. Stayed at Gore Bay Sat 25th May 2019 (allowed up to 2 nights then), very nice pull ins by rest rooms/restaurant area overlooking water, next to one other MH.
In case it helps for future planning, and of course remember to write up your experience as that's how everyone benefits from these free resources to find camping locations, we use: Freecampsites.net Ioverlander.com and Campendium.com There are a few newer ones in the mix now, but to get full benefits appears you have to subscribe and pay for service: FreeRoam and The Dyrt.
Hope some of the above, mixed in with when you are doing in the US one day again, using BLM, USFS MUVU, Arizona Trust Lands, Wildlife Refuges.
Other things to consider are churches, marinas, as well the usual big box stores, truck stops etc.
Happy Travels, we had an awesome trip last year across from Alberta through Canada to Newfoundland (the rock), hitting the big lakes on the Canadian side and then back through on the south side in the USA. Found the south side USA more boondock friendly near the lakes than the Canadian side again just FWIW.
PS: I haven't checked but have you scanned Boondockers Welcome/Harvest host maps to see if anyone listed on their for the island to O/N?
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