AFAIK, unless you have a government issued "indigenous person" id, you pay the going area price for whatever you buy. Only the aboriginals get the cheaper price/rate.
That may have changed, but that's how it worked a few years ago. Used to live and drive near the Brantford 6 Nations area when we lived nearer to it, and pulled in once, only to find that we didn't qualify for the much lower price displayed on their price signage.
Maybe some of the on reserve stations (Mohawks?) don't care any more, and sell it to everyone now?
Got a Costco card? There must be a few along your route, and they're probably the cheapest, just off the 401.
Official government blah blah
https://www.fin.gov.on.ca/en/bulletins/gt/3_2011.html
Mike. Comments are anecdotal or personal opinions, and worth what you paid for them.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)