Upload & Sell: On
Taking pictures in the cold is all about keeping the batteries warm, having access to the shutter with frozen fingers, avoiding breathing so that it fogs and freezes up the lens, and not getting frostbight on your nose because you are looking through your viewfinder your nose touchs the screen.
Bring even more batteries. Bring gloves that work in mitts. Bring something for covering your nose. Bring more cards - they don't weigh much. And why ration yourself.
I would bring 7d. I use it in the cold and have not had any trouble. I would consider bringing a spare body. They don't weigh much. I would bring my 5dii because it shares batteries with 7d but that would change my lens selections.
70-200 2.8 LIS is good. If I were going to add something to this I would bring a 1.4x. I have used this combination in a pinch and it is good. Personally though, I would be inclined to leave it behind and bring the 100-400 for reach. 100-400 is lighter and longer and likely most of shots will be in the day time, and avoids fiddling with 1.4. Tough choice, IQ on 100-400 is better than IQ on 70-200 with 1.4x, but 2.8 is useful. But I would go 100-400.
24-70 is a bit long on 7d with no IS. 17-55 2.8 IS would permit getting the northern lights and more low light shots than 24-70. I think I would change this plan. You will miss lots of shots on 7d close up with 24. And the IS will be helpful. If I brought the 5dii as backup body, I would bring a 24-105 and use the 7d for backup.
Try to find room for a better tripod. You wil have lots of difficulty with northern lights etc with a gorrila pod.
Thats my thoughts. Have fun.