Many gun shops will ship/store a gun for you. Find one where you intend to enter Canada, and ship to where you'll return to USA. It'll cost a few bucks, but prevents a lot of unpleasantries.
When we entered CA on the way to Alaska, I was grilled in depth about owning guns, where they were stored, if under lock and key, if we felt safe without our guns, etc. I finally told the offending agent that my guns are all back home, safe and sound, and if she wanted to search the camper, have at it. Otherwise, let me proceed.