Native Peoples

Native people are often in a relatively unique situation when it comes to going vegan, and while it can vary from region to region, generally speaking it is significantly more difficult for them due to their marginalized status and reliance on subsistence hunting/fishing for survival, as well as less pressing from a moral perspective to encourage them to do so because the source of their animal products is usually both more sustainable and less cruel than typical animal agriculture: in sum, it makes promoting veganism to native populations a poor bargain in terms of effective activism.

You'll have a hard time getting very far or convincing many people, and even if you do succeed the payoff in terms of animal suffering prevented for success will be much smaller than having convinced somebody from the mainstream/dominant culture to go vegan. So in short: please don't waste your precious activist time on trying to convince people for whom it may be nearly impossible to go vegan. Focus on the low hanging fruit from within mainstream society where going vegan is much easier and more productive.

Food Access

Similar to Food Deserts, native people can have food access problems that make going vegan more difficult for them.

Regional Food Prices

In many regions where native people live, particularly near or in the arctic circle (wherein around 10% of the inhabitants are native), most foods must be imported and prices can be astronomically high for things that many vegans (and others) take for granted in regions closer to production.

"We've fought to be more equal to the rest of Canada in terms of purchasing food or other items, but there seems to be an invisible border somewhere that once you cross that line, the cost of food or merchandise doubles or triples in cost," Iqalukjuak[1]

A recent Canadian study found huge differences by region,

Food insecurity was most prevalent in Canada’s North (especially Nunavut) and the Maritimes in 2014. In Nunavut and the Northwest Territories, the prevalence rose to the highest levels observed since monitoring began in 2005, 46.8% and 24.1% respectively.[2]

However, the study didn't include First Nations people on reserves, where the problem is likely even worse than in cities.

Although on-reserve First Nations people and homeless peoplex comprise relatively small proportions of the populations in each province, their high levels of vulnerability to food insecurity must mean that the true prevalence of food insecurity is to some extent underestimated because of their omission.[3]

Efforts are underway to better quantify the problem on reserves (First Nations Food, Nutrition & Environment Study[4]), but we can only assume food security issues on reserves are much more severe.

While somehow fast-food companies seem to have managed to bring slightly more affordable (albeit unhealthy) food to the region, these obviously don't provide viable vegan options for most people.

There are very few viable local food options. While agriculture in these regions is possible, it's very difficult and often requires infrastructure-heavy modern techniques like greenhouses and even grow lights to get a head-start on sprouting which may not be accessible to people in poverty. Foraging for plant foods is sometimes an option, but may provide limited nutritional value (berries aren't nutritionally adequate, and many foraged greens are richer in oxalates than cultivated vegetables).
Meanwhile, the innately non-vegan options of hunting and fishing are essentially free for native people and provide food availability year-round: it may not be optimally healthy, but risk of malnutrition is of principle concern for people suffering from food insecurity.

In theory it is possible to import food more efficiently including non-perishables, even circumventing grocery stores, but this represents a major political and infrastructure issue and requires organizing coops, etc. For this reason, focusing vegan outreach on natives isn't the low-hanging fruit of "it's easy to go vegan" that it is for a solvent person in a modern city. While it might be productive vegan outreach to go to these regions and organize coops to sell vegan food at affordable prices, simply telling native people not to exploit the only immediately accessible food resources many of them have (hunting & fishing) is probably wasted effort and may only serve to antagonize.

False Economy of Animal Products

High meat diets can pose health risks, even among native people like Inuit who have had them for generations[5]. There's significant unwillingness to accept this fact among people who appeal to tradition, but the evidence for the health of plant based diets seems to be applicable across wide genetic variation (although possibly to varying degrees). Claims of poorer health on more plant based or grain based diets are more likely to be attributable to other factors that came with those diets, such as more sedentary lifestyle or consumption of highly processed oily/sugary junk foods (which happen often to be plant based, but which do not by necessity typify plant based foods).

It can be argued that saving money now by hunting or fishing, or simply eating fast food, can cost more money later through the deleterious health effects. While health arguments can still be strong, having enough food to eat and feed your family today is always going to be a more pressing issue to people than an abstract risk in the future; even health can be seen as a matter of privilege despite the false economy of unhealthy foods because if you can't afford it then you may be trapped despite that knowledge.