It seems call
It seems writing or calling both Canadian and U.S. Customs is the simplest method, and you should ask for a written answer, to keep with you.
I like firearms but when crossing into other States, I go to that State's A. G. Website and read the laws for myself.
I've seen people in Court who violated laws, because they believed the Cop or a Deputy Sheriff that told them it was legal to do what they were arrested for, which does not hold water with judges, so go yourself to the direct source, not other photographers, stores, photographers associations like Photrio.com or others.
Good luck.
So far, this whole thread is then more or less useless, considering we only got tricks or loopholes. I agree that looking up at the laws itself is the answer. That's unfortunate it seems quite difficult to get those rules thru the net, though. Do you have a link?