Emily VanCamp has signed on to play the female lead in Captain America: The Winter Soldier.
The character has yet to be disclosed, though speculation is that Sharon Carter will play alongside Steve Rogers. Carter is the niece of Peggy Carter, played by Hayley Atwell in the first film. Though the character was originally the sister of Peggy, she has since been "retconned" to make sense in a modern continuity (though that timeline is still a bit of a stretch if the Winter Soldier will be set in present-day).
Captain America: The Winter Soldier has a release date set for April 4, 2014.