There are three characters who currently exist as part of the Marvel Cinematic Universe that, at one point or another, have taken up the mantle of Captain America in the world of Marvel Comics: Steve Rogers (Chris Evans), Sam Wilson (Anthony Mackie) and Bucky Barnes (Sebastian Stan), to be exact. Of course, during the aftermath of the events that transpired in this year's Captain America: Civil War, none of them are going to be carrying the title of the Star-Spangled Avenger. Civil War co-director has likewise confirmed that Steve dropping his Cap shield at the end of that film was him "letting go of that identity" - for now, anyway.
Evans is expected to don his red, white and blue superhero costume again in the upcoming Avengers: Infinity War, for the start of the big battle against the enemy whom Earth's Mightiest Heroes have been unknowingly fighting since the Avengers first assembled in 2012: the Mad Titan himself, Thanos (Josh Brolin). That hasn't stopped fans from creating art showing what Sebastian as Bucky could look like in the Captain America costume - or, for that matter, how Mackie as Sam would look in a real-world version of the character's Cap suit from the Marvel Comics (see above).
Artist Aiko Aiham has created fan-art of characters from both the MCU (including, their own take on Bucky as Captain America) and the DC Extended Universe (including, Ben Affleck's Batman and Jared Leto's Joker). You can check out his artwork showing what Mackie could look like as the Sam Wilson Captain America, below:
For those unfamiliar: Sam Wilson took up the mantle of Captain America from an aging Steve Rogers in the All-New Captain America comic book series that launched in 2014, pitting the former Falcon against the threat of (what else?) Hydra. Naturally, if the MCU does put Sam in the Cap costume, things will have to play out differently, following the events of Civil War on the big screen and the (at least, temporary) dissolution of the Hydra organization, in Agents of S.H.I.E.L.D. season 3 on the small screen. Not to mention, Evans' enthusiasm for the future of the MCU is stronger than ever right now and he seems perfectly content to keep playing Steve Rogers for as long as Marvel Studios will allow him to.
Mackie, for his part, has indicated that he would rather stick with Sam Wilson being Falcon in the MCU and not push Evans out of his spot as Captain America, allowing for Falcon to continue popping up in other MCU superhero's "solo" movies (including, the Black Widow film that may finally happen at last in Phase 4 of the MCU). Nevertheless, as fan-art such as that above illustrates, if Mackie ever does get to portray the Sam Wilson Captain America, he should look pretty dang cool while doing so.
Captain America: Civil War will be available on Digital HD on September 2nd and on Blu-ray on September 13th, 2016.
Doctor Strange opens November 4, 2016; Guardians of the Galaxy Vol. 2 – May 5, 2017; Spider-Man: Homecoming – July 7, 2017; Thor: Ragnarok – November 3, 2017; Black Panther – February 16, 2018; Avengers: Infinity – May 4, 2018; Ant-Man and the Wasp – July 6, 2018; Captain Marvel – March 8, 2019; Untitled Avengers – May 3, 2019; and as-yet-untitled Marvel movies on July 12, 2019, and on May 1, July 10, and November 6 in 2020.
Source: Aiko Aiham