According to a recent post by Chris Priestly on the BioWare forums, Mass Effect 3 will require EA’s Origin service, both for physical and digital PC copies. Luckily, though, it will not require a constant connection to the Origin servers for the single-player campaign, just a one time authorization. The multiplayer component, however, will need a constant Origin connection.
The prospect of a Steam appearance is looking fairly slim. Initially it was said that “Mass Effect 3 will be available on Origin and a number of 3rd party digital retailers.” Steam is not one of those retailers, with Priestly stating that, “Steam has adopted a set of restrictive terms of service which limit how developers interact with customers to deliver patches and other downloadable content.”
Not too much to be surprised about, honestly. EA has pulled quite a few of its titles from Steam, and has been pushing Origin hard over the last year. Hopefully this move doesn’t turn players off of what is potentially an amazing game.