If you want to discuss this problem in terms of causes, jurisdiction and possible solutions, I would love to.

I don't know if you have the same problems in Ontario as we have in the west although I suspect you do, at least to some degree. Our biggest problem is the packs of feral/wild/stray dogs which for all intents and purposes, might be better off dead. Fortunately (from my perspective) we don't kill them just for being, although there are exceptions and even some bands pay $20 per tail just to get rid of them.
The problem is that they come into town and mingle with our dogs and some people even feed them... Just once, and you know how that goes. So then what happens is that children who haven't yet learned are sometimes cruel to them and they think that's ok because they hear adults speaking negatively about them.

I wish we could solve the problem(s) right here and right now but the chances of that are about as likely as solving all of the other Native problems in North America...
I'm not saying there is no animal cruelty on reserves but then again, some people think it's cruel to eat a cow, or a moose.
Personally, I never witnessed any worse cruelty than off-rez - some of the white guys I went to post-secondary with used to take pleasure in collecting cats on Friday night and torturing them for entertainment. I got into a lot of trouble for defending the cats back then, but we didn't have facebook to out them at the time.

I don't know what the solutions are but I don't feel this is an issue to single out the Natives who, to a large degree, would probably be happy to implement population control by eating them (I've done this with one of our elders). If only that weren't viewed so "inhumane" by "others".

N.B. Wild dogs like the ones I'm talking about who live in the bush are mostly raised on wild game and so no need to think they taste anything like Purina.