Warning: potentially major spoilers for Captain America: Civil War are ahead!
As anyone who’s read Ed Brubaker’s run of the Captain America comics knows, Steve Rogers met a gruesome fate following the original Civil War story, being gunned down shortly after surrendering himself to the authorities. Since this is the world of comics, Steve was back in action a few years later, but his "death" is still one of the more shocking moments in Marvel history. If a recent rumor is to be believed, that moment will be adapted next year in Captain America: Civil War. Now, because Chris Evans has already been confirmed to appear in the Avengers: Infinity War movies, we know Steve will be back to fight another day (unless his role is just through flashbacks). That said, this same rumor indicates that someone else will inherit the star spangled mantle during his absence.
In the report, it’s mentioned that at Steve’s funeral at the end of the movie, there will be a scene showing three people lifting up Steve’s shield, implying that one of them will become the new Captain America. These folks are: Bucky Barnes, a.k.a. The Winter Soldier; Sam Wilson, a.k.a. The Falcon; and Sharon Carter, a.k.a. Agent 13. Obviously we won’t know for sure if this information is legitimate or not until the movie hits theaters, but these three are certainly choices to carry on the Captain America legacy. Assuming Steve does indeed die (or simply disappear), let's look at how probable it is that each of these three candidates could become the new Star Spangled Avenger.
Bucky BarnesTo say Bucky Barnes’ life is in turmoil is an understatement. After decades of being the brainwashed Winter Soldier, he finally overcame HYDRA’s control in Captain America: The Winter Soldier and is on the run. He’s not (and probably never will be) the same Bucky he was in Captain America: The First Avenger, but as seen in the Civil War trailer, he’s trying to seek redemption for his past crimes. To no one’s surprise, Bucky will be siding with Steve (or to put it another way, be against registration) during the superhero conflict, and those two will eventually partner up to deliver a beating to Iron Man.
Odds That They Will Take Over For Cap: Pretty high. After Steve "died" in the comics, Bucky was the one who took over as Captain America, and even after Steve "came back to life," Bucky held onto the identity for a couple more years. So it would make sense for the movie to stay faithful to the source material and have Bucky inherit the mantle. Even if we just analyze this purely from an MCU standpoint, Bucky is Steve’s oldest friend, and even though they’ve been apart for over 70 years, one would imagine Steve would approve of Bucky continuing in his place. Plus, since Bucky’s trying to atone for what he did as the Winter Soldier, being the new Captain America would help balance the scales.
Sam WilsonSam Wilson hasn’t known Steve Rogers are long as Bucky has, but the two of them still share a special friendship. Meeting in Captain America: The Winter Soldier, the two of them worked together with Black Widow, Maria Hill and Nick Fury to root out HYDRA from S.H.I.E.L.D. and stop their insidious plot. As seen in Avengers: Age of Ultron and Ant-Man, Sam is now in full swing fighting crime as The Falcon, as well as a member of the New Avengers. Sam will remain loyal to Steve during Captain America: Civil War, though as he mentioned in the trailer, he’s getting tired of the people shooting at Cap shooting at him, too. We’ll also finally see Falcon’s sidekick Redwing make his debut, though as a drone rather than an actual bird.
Odds That They Will Take Over For Cap: While not as high as Bucky’s, there’s still a decent chance Sam could take over. Sam Wilson is currently serving as Captain America in the comics following Steve being aged to an old man. Ignoring that brief shot of Sam in Avengers: Age of Ultron, we’ve seen him in action as Falcon in two movies so far, and Captain America: Civil War will make three. That uniform of his could easily be given a red, white and blue paint job. However, Falcon has proven to be a popular character in the MCU, and it might be weird to suddenly take the Falcon identity away from him after only a few adventures. Granted, Bucky is known as Winter Soldier, but it would be easier to transition him away from that moniker than it would be for Sam and Falcon.
Sharon CarterSharon Carter, a.k.a. Agent 13, was arguably the most mysterious supporting character in Captain America: The Winter Soldier. After appearing in the first half of the movie, she was seen later on as one of the non-corrupt S.H.I.E.L.D. agents who was inspired by Cap’s speech and helped fight the HYDRA operatives. We last saw her applying to be in the CIA, and she’ll return in Captain America: Civil War to fight alongside Steve since the two of them have "similar moral compasses." Although it hasn’t been made crystal clear to the casual viewer, hardcore fans know that Sharon is related to Steve’s World War II love Peggy Carter, but unlike in the comics, we may not see Steve get romantically involved with this member of the Carter family.
Odds That They Will Take Over For Cap: Very low indeed, considering that Sharon never served as Captain America in the comics. Even though Sharon is an important person in Captain America’s life in the comics, both as a love interest and a partner in the field, they don’t have that strong relationship yet in the MCU. It would be an unusual move to give the identity to someone the audience doesn’t know that well, especially when Steve is much closer with Bucky and Sam. That said, considering that no woman has ever served as Captain America in the main Marvel universe, it would be an interesting left turn for the MCU to break new ground by giving Sharon the mantle. That would undoubtedly that would take moviegoers by surprise, whether they’re longtime fans or normal viewers.