FUNimation's released portion of the Attack On Titan English dub cast 

So Lan Fan from FMAB is Mikasa. That seems like a good match to me, both being protective of certain people. (Eren and Ling respectively.)

So have they purposely not announced Eren or Armin?

^They are releasing the cast bit by bit. It will probably be announced tomorrow. :)

One would imagine, going from characters like Levi to Mikasa implies they are dropping serious stuff now rather than characters like Shardis that have maybe three minutes of screen time.