Towns like Cranbrook, Canmor, Prince George, Whitehorse will have better grocery shopping than Banff, Jasper and smaller. If the town is big enough to support a Canadian Tire, the groceries will have a decent selection and pricing.
Sometimes, though, the resort towns have groceries with specialty items, the kinds of things that well-off vacationers eat in their rented condos. I've shopped in Whistler, Lake Louise and Jasper. I prefer bakeries and delis.
On one trip, back in the 1980s, I would buy a whole frozen chicken from a small town grocery along the Alaska Hwy (and even in Eagle AK), let it thaw in the cooler for a day or two, and then cook some sort of cachiatori in the pressure cooker on the gas camp stove.
Later I bought a small 1.5 L pressure cooker that let me cook small cuts of chuck in a few minutes, just enough for 2 people and no left overs (this was car camping without a fridge).