When you cross bury the bear spray in the bottom of your camping gear. Repeat after me "Bear spray is not a weapon, it's a camping tool.".
If they ask you you have any weapons say "No, just camping gear."
If they ask if you have bear spray, say "Yes sir, packed in with the rest of my camping gear.".
If you get an asshole customs officer who wants to seize it, ask VERY, VERY politely to speak with a supervisor about his interpretation of bear spray as a weapon.
If you get brushed off, again politely ask to speak to a supervisor. It's legal to own and purchase in Canada as camping gear. And a supervisor will 99/100 back yiou up, especially if you're being polite about it.