Just did some playing around in a game by myself and found out that you can land your troops on - and have them move around - most of the Arctic, enabling you to do such things as cross from Greenland to Northern Canada and vice versa.
For some reason though you can't go onto the Arctic ice north of Russia, which I find a bit odd.
Additionally, Antarctica can also be traversed by land troops.
Anyone ever used or fought battles in the Arctic or Antarctica in a proper Multiplayer game?