Ah...I think I finally found the film I've been searching for.

I think I remember seeing this film quite a few years back, but I need confirmation that I've got the right one.

Here are some scenes I remember:

Near the beginning of the movie (I think), a sled dog gets killed by a small pack of wolves. I remember this scene made my heart beat violently. It was very painful to watch.

The main dog gets put into a death fight with a black pitbull or some sort of vicious dog.

The main dog finds a nice new owner, and near the end of the film, the owner is killed by some guy who shoots crossbows at him. The dog pounces on the offender and gnaws his throat.