Alot of interesting suggestions, not to mention hilarious.
Anyway, I think if they're gonna put a specific animal in the game and make it interactable, it has to have an impact in some of the missions. For instance, if they're gonna put dogs in the game (wich is pretty much official that they will) there will be some missions where you have to get past some of them. This could mean killing them, or perhaps using your skills to sneak past them.
The idea of bears in the wild sounds cool at first, but then again, it feel as it would just get annoying to stumble upon bears whenever you're out in the wild with your dirtbike.
A very interesting suggestion someone brought up was a zoo. Again, if they're gonna build a zoo in the game I can't wait to play the potentially creative missions that takes place in there. On the top of my head all I can think of is throwing bad guys in to different animals' habitats. Or maybe dress up as a zookeeper, steal an ape and train it to assassin someone.