As far as I know, bringing bear spray from Canada to the US is not problem. I thought it was a problem bringing it from the US to Canada because we were flagged but able to sign a form and pick it up later when we went back to the US. (This was a while ago and may have been pepper spray.)
I saw this on Facebook and it sounded like the guy had knowledge:
Canadian Customs will allow bear spray approved by the United States Environmental Protection Agency (USEPA) to enter Canada. Bear repellents are not considered prohibited in Canada, but the specifications state that the bear spray must bear USEPA on the label. However, bear bangers (with explosive) are currently not permitted. Just an FYI.
I also saw there is a "sharing shack" for coolers, bear spray, etc. Located just east of highway 206 and Highway 2 in Columbia Falls.
Jay
Currently 98F.