According to the New York Post's Page Six, Anna Kendrick (Up in the Air, The Twilight Saga), Felicity Jones (Cemetery Junction, Like Crazy) and Imogen Poots (Fright Night, 28 Weeks Later) are considered frontrunners for the role, which isn't identified but is presumably that of S.H.I.E.L.D. Agent Sharon Carter.
Directed by brothers Anthony and Joe Russo, Captain America: The Winter Soldier is believed to be based on the Marvel comics storyline of the same name by Ed Brubaker, Steve Epting and Mike Perkins.
In the celebrated arc, it was revealed that Captain America's World War II sidekick didn't die in the same 1945 explosion that left the Sentinel of Liberty in suspended animation in a block of ice. Instead, an amnesiac Bucky actually survived the explosion and, fitted with a bionic arm, served as an assassin for the Soviet Union known as the Winter Soldier, a secret revealed in the present day only after he seemingly killed the Red Skull and launched a terrorist attack on Philadelphia. His memory restored with the help of Captain America and the Cosmic Cube, he reteams with his former partner and even assumes his mantle following the apparent assassination of Steve Rogers. Sharon Carter, the niece of Captain America's wartime love interest Peggy Carter (portrayed in the first film by Hayley Atwell), plays a central role in the storyline.
While Anthony Russo has so far avoided directly answering questions about the sequel, he did reveal last month that it's at least heavily influenced by Brubaker's story. “I can say in general that there’s sort of a darker, edgier sensibility at work there that we found appealing, and that is going find its way into Captain [America] in the modern day," he said.
Captain America: The Winter Soldier opens April 4, 2014.