In order to get in the Alaska system, you will need to play the single player campaign. This system along with Tohoku are the only ones that cannot be accessed if you're playing the multiplayer mode. You will have the possibility to navigate to Alaska using a tunnel located next to the mines. I suggest you use Google search engine to find additional information, guides and tips.
The answer is no, you cannot skip the early stages of the game. You will need to follow the story and the levels as they are.
How can I go in Alaska system?
In order to get in the Alaska system, you will need to play the single player campaign. This system along with Tohoku are the only ones that cannot be accessed if you're playing the multiplayer mode. You will have the possibility to navigate to Alaska using a tunnel located next to the mines. I suggest you use Google search engine to find additional information, guides and tips.