Great call, Tony. If a (wingless) female could be found, then you could probably get a species ID.

So this one's a male, then? I'm a real newbie at moths. I'd only been able to narrow it down to the family Geometridae based on its silhouette. Now with your brilliant help, I bet it's O. brumata, based on these images of the three species of Operophtera occurring in Western Canada. Wouldn't you agree?

seems reasonable for this specimen (dorsal view). However, the other specimen (ventral view) is not brumata. Note the little spot (discal spot) on the hind wing. This spot can also be seen on the dorsal photo of the CBIF image you referenced. O. brumata lacks this discal spot; spot certainly present in bruceata and I believe it is also present in O. danbyi. Thus if you have 1 species it is not brumata, but if you have 2 species then one could be brumata.

I'm not convinced that dark area is a discal spot. It looks to me as though it could be simply part of the vein in the wing. And though I neglected to photograph the dorsal view of that specimen, I did look at it under a loupe, and I do not recall it having any spot; it certainly did not have any elaborate markings like O. bruceata. My description of it at the time was "non-descript greyish brown moth." Another O. brumata came by and visited my sliding glass window today (definitely no spot), but my dog ate it before I had a chance to photograph it!