The upcoming sequel follows Cap in the modern-day as he deals with the return of his long thought dead ally, Bucky Barnes, who has returned as a Soviet-programmed super assassin intent on taking him down.
There is no firm details on how Falcon will be brought into the mix but I suspect he will be a SHIELD Agent assigned to escort Cap, much like Agent Coulson once did with Tony Stark and Thor. It's the most logical way to reconcile the character's close connection to Cap with the more hands-on role that SHIELD plays in the Marvel Movieverse. I would also imagine his rather excessive costume will be binned; much like Hawkeye's.
Anthony Mackie is currently in talks to play the role and if they sign him, it would be a great coup for the sequel. Mackie's more recent high-profile work includes The Hurt Locker, The Adjustment Bureau and Abraham Lincoln: Vampire Hunter. Oscar-worthy projects aside, nothing that really grabs the public's attention, but he always brings real presence and personality to his roles. Should he land the role of Falcon, and I sincerely hope he does, I would expect more of the same.
Captain America: The Winter Soldier will be released Summer 2014.