Canadian here with a severe peanut/nut allergy so I can only speak towards my experience. I've been fine with common ingredients from any brand. Avoiding anything that says "may contain" is to the extreme (in my opinion, but to each their own), but most ingredients do not have it listed. It's best to read the ingredient list, it'll usually say in bold (in both english and french) the common allergens and if it may contain something. If you want to buy something pre-packaged, there's a lot of things in any grocery store that has the "peanut free" symbol on it.

The best thing to do when cooking as well, is to make sure all surfaces are wiped down and any utensils are cleaned (if they had come in contact with potential allergens). The best thing to do is to keep a list of the ingredients as well to let the person know (sometimes people think XYZ isn't a nut, so I usually ask before I eat a dessert).

If you do want to be extra safe there's a lot of brands with mixes you could order online (I haven't tried any of these yet), such as: https://enjoylifefoods.com/collections/baking-mixes
https://sweetsfromtheearth.com/shop/
etc