Back when I was growing up in California they were always called "camper shells" because it was just a shell and didn't have any amenities like a slide-in camper. Over the years I've had to adjust what I refer to them as, both due to regional as well as generational changes in what people called them. Shell, camper shell, topper, cap, etc. Canopy seems to be another PNW-ism and Canadianism.But a national manufacturer doesn't get you to regional differences, which is what this thread is about (that and age differences).
Quite frankly, again except for the fact this is a Colorado/Canyon forum, the term "camper shell" to me would mean some old stripped out truck camper--a potential project. But because this is for Colorados and Canyons, it's sort of obvious what's referred to. Also, I've never heard of a topper.
How about referring to freeways as "the <number>?" "Take the 5 to the 101..."