I've wondered that as well, ever since I heard the different stats on US National Parks. In the USA, black bears basically cause property damamge with the exception of Glacier National Park (on the Canadian border) where there are serious human injuries at times.
BPing in California decades ago, I'd imagined that black bears were wimps because before 1850 grizzlies killed them and after 1850, humans hunted them, so they were never the dominant thing in their range. Whereas grizzlies, since the last ice age, were the dominant thing around except where they intersected with humans in the last 200 years (and those bears aren't around anymore). And here in Alaska, black bears are really wimpy. I've seen a bunch but only because I'm out a lot and blackies are ALWAYS heading the other way, fast, when I see them. And I see more grizzlies despite there being 10 times more black bears in this area. So blackies are wimps AND very shy.
I don't know why it is different in Canada. Are there areas in which black bears are dominant (no grizzlies)? Or somehow, they just have slightly different genetics? I've seen enough of different breeding lines of sled dogs (much less domesticated farm animals) to know that seemingly complicated behavioral traits (including aggression) can be strongly genetic. Consider a retriever's or pointer's behavior.
I'd note that as you go north, there's a shorter season for eating but you need to eat more for the longer winter. So maybe a black bear needs to be aggressive in order to put on enough fat for hibernation. In California, black bears can eat huge amounts of acorns with no risk, no competition. Where I am in Alaska, the summer is incredibly productive with berries, rodents, and dead fish, so it's easy to put on weight. Maybe in the less productive Canadian Rockies, a more aggressive bear is better suited to claiming the best patch of berries, etc.
In pigeons, aggression is a ONE GENE TRAIT which I found amazing when I read that research paper. The outcome of two pigeons facing off over a bread crumb is completely predicted by whether the birds have 0, 1, or 2 copies of the aggression gene. When the environment gets tough, the bears get tougher?