AT 'Brother...

Okay, I'll try to be as helpful as I can. Well the first thing that caught my attention was the coloring, its really nice and very detailed, the trees and snow are amazing. Let's start with the brown dog at the right. The head and neck are too big, both together are almost as big as the back. Other than that, the body and pose looks good.
About the white dog at the left; the chest is too round and a little big, more like a human chest. Dogs chests are more... like this. static2.dmcdn.net/static/video/639/133/29331936:jpeg_preview_medium.jpg?20111011203447 like a square. Of course chests have muscles and that all, but they're not so obvious at first glance.

About his face; There's a strong black line after the eye. There's no need to exaggerate the muscles that much in the face. [link] As you can see here, there are no lines. at all.

Your coloring is amazing, coloring snow is a hard thing but you managed to do it really well, plus the lights and shadings and stuff are really good.

Also remember that the stuff close to your eye should be blurred, like when you place something just in front of you. It looks kinda blurry, same with far away things.

I hope I helped you.