Are we talking brown bears or black bears?
Brown bears are violently territorial and will attack you for being in eyeshot.
Black bears are basically giant racoons and will move away from people - especially if you’re making loud noises and making yourself look big - because they don’t want that smoke. They’ll only get aggressive if you surprise them or get anywhere near their younglings.
I’d probably take a black bear over a lot of dudes. As long as we got a good hundred feet or so of distance, Mr Bear and I ain’t gonna bother each other.
The Astartes would totally be on the side of Sauron. They’re brainwashed child soldiers filled with xenophobia and hate. Definitely makes more sense for them to be Orcs - actually that’s basically what Orcs are in Tolkien.