It'll be Steam by default. Stardock lacks the means at this time to fight Steam. If they want multiplayer and other online features, their best way to go about adding those to the game is to use Steam and Steamworks. Alternatives cost time and money (and lots of it).
From what I understand, when the alpha begins, you will be sent your Steam keys. Not a nano second sooner.
If you have any further questions, feel free to ask.
