I am a long time Alaskan hunter, brown bear hunter, and professional Alaskan bear photographer. I lived on Kodiak Island for many years and have lots of experience with these guys.
If you can find a copy - look for a video called 'Take a Closer Look'. It is a neat brown bear video identification guide that will teach you how to recognize brown bears. This is handy since a three year old has really big ears, and, a trophy 10 footer will have tiny ears compaired to the size of the head. Knowing the difference means you can scare away the young one - won't work with the older one. Video is worth it's weight in gold for understand bear body language.
12 ga with sabot slugs will put down a brown bear just as good as any rifle at close range - however - do not count on your first shot sending it to heaven. You need to break bones and hit vital organs to stop them - they are built very strong and powerful and can recover from a lethal shot for several minutes. One swipe and your life is ruined. Rule of thumb when bear hunting or protecting yourself from a bear is to keep shooting until it stops moving.
You cannot bring your retractable shotgun to Canada - these are classifed as assault weapons. Only certain shotguns are allowed. When you cross the boarder be sure t have a nice pretty vent rib barrel used for skeet or bird hunting. When it is time to hike - put on the smaller yet still legal barrel.
Your first two or three round coming out of the 12ga should all be sabots. After that OO Buck. Reason being if a bear is charging you, or, you have to shoot it off a buddy - with a sabot you have a good chance of being somewhat accurate. And after your 3rd sabot is expended you will be in 'panic fire mode' and the OO Buck should get you more hits.
Don't cheap out and just buy a box of each and hope for the best. You won't do anyone any good unless you practice with the sabot and OO Buck. Standard shotgun qualification course for the military is 40 rounds............ so at least do this.
What ever you do - do not tell 'em at the border you have the shotgun for bear protection. Right now they don't let anyone in with Bear Spray for fear someone might accidentally spray another person in the woods thinking they might be a bear. Gimme a break!
The Canadian government has a web site set up just for folks visiting with firearms. Be sure to read up on the latest and greatest. I do know for sure you cannot have a shotgun with a pistol grip, colapsing stock, or a heat shield.
Hope this helps!