Thanks to CBM, we now know who makes up each of these teams because of some promo art for the film that they managed to get their hands on.
On team Iron Man, we have War Machine, Black Widow, Black Panther and Vision. He may not be in the image, but we also previously learned that Spider-Man will be on his team as well. Then if Bruce Banner is in the film, we all know whose side he will choose.
On team Captain America, we have Bucky Barnes, Sam Wilson, Hawkeye, Ant-Man, and Sharon Carter. Scarlet Witch, who is also not included in the art, but will be fighting for Captains team.
You will find a video below from Mr. Sunday Movies discussing the teams.
“Captain America: Civil War” picks up where “Avengers: Age of Ultron” left off, as Steve Rogers leads the new team of Avengers in their continued efforts to safeguard humanity. After another international incident involving the Avengers results in collateral damage, political pressure mounts to install a system of accountability and a governing body to determine when to enlist the services of the team. The new status quo fractures the Avengers while they try to protect the world from a new and nefarious villain.