as I am in the east, and never had bear spray here, I dont really know the laws about it. I did buy some 20 odd years ago out in British Columbia, in grizzly land, for hiking, but thats the only time I've had some (that bottle is still in a closet in fact) so am not up on current laws in any Provinces to be honest, or cross border stuff either.
I have cycled through bear areas in both the US and Canada. My experience:
1. In 2016, I bought bear spray in BC a short distance front Banff after seeing multiple "trail closed due to bears" signs. Purchasing this required me to sign and turn in declarations that essentially said "I realize bear spray is a weapon, and promise to only use it on bears". So there was an official record of my purchase. I didn't declare it but don't believe there was any issue bringing this across the border to the US.
2. Some years before I started a trip in Haines Alaska and crossed into YT. The Canadian border guards started with standard questions about "any weapons" but then specifically asked "even bear spray". The way they were asking seemed to give mixed messages of (a) cyclist you are a fool to travel in this part of YT without bear spray and (b) if you did have it, there would be special rules/restrictions you should follow...