Before we begin with my list of Heroes- With the revelation that Sony will allow Spider-Man to appear in an MCU movie before Appearing in a 2017 Sony (solo) Spider-Man movie, My theory is that Spider-Man may appear in some capacity in Captain America: Civil War and maybe even [The Avengers: Infinity War](movie:738027) part 1 & 2, after his Sony solo film. Civil War begins filming in April (just over a month from now) so they would have to cast Spider-Man very soon!
Meanwhile, Marvel has a slew of other heroes it has reclaimed the rights to that should make an appearance in the upcoming Captain America 3: Civil War and Marvel should take full advantage of their roles from the original comic: Civil War.
1. The Punisher/Frank Castle
There are theories that the Punisher was in [Captain America: The Winter Soldier](movie:254973) and drove the moving truck that plowed through the Police Cars and saved Nick Fury...
"The man who drives that truck," jokes Joe Russo, explaining he could be the subject a Marvel One Shot short film, "is very highly trained."
If indeed that was The Punisher, I would like to see him appear again to aid Cap and the other Anti-Reg Heroes in this movie. He should be played by Ray Stevenson-since Ray already works for Marvel Studios as "Volstagg," in the Thor franchise of films. I'm sure Ray would like to play a bigger part than Volstagg who- as a character, is probably done after [Thor: Ragnarok](movie:956858). Ray could do the part (of Punisher) justice by playing him in a well written, seriously directed film.
2. Matt Murdock/Daredevil
[Daredevil](movie:47230) will be introduced on Netflix this April (2015.) Shooting for Captain America: Civil War also begins in April. Since Charlie Cox is already done filming for the Daredevil series, there's no reason why he can't appear in the Civil War movie as both Matt Murdock: an attorney trying to help those Heroes against Registration and as Daredevil a member of Cap's Team against Iron-Man.
I already expect that both Ant-Man and [Doctor Strange](movie:559685) may have cameos in this movie as will Black Panther (in costume). It is rumored that a villain appearing in this film will be Doctor Strange's main antagonist in his upcoming solo film. Ant-Man (Scott Lang) would be Anti-Reg while Hank Pym would be on Iron-Man's side of this fight.
3 & 4. Luke Cage & Jessica Jones
The timing for this one might be a bit tricky. Krysten Ritter will play Jessica Jones on Netflix in (Fall?) 2015, meaning they have to start shooting this soon for her series to be out in time. Mike Colter, cast as Luke Cage has more time in his schedule as his series starts after Jessica Jones (April 2016?). He may make an appearance on Jessica Jones' show (in 2015) prior to his own but he should have time to shoot scenes in the Civil War movie which begins filming in April, 2015. When the film releases in May 2016, It will be a golden opportunity to showcase both Jessica Jones and Luke Cage. Since Luke Cage was experimented on by Stark Industries, Luke Cage aka Power-Man would be an easy add-on for the Anti-Reg side.
5. (Last but not least) The Spectacular Spider-Man!
Look for Spider-Man to be a big part of Civil War since he was a central part of the comic book storyline. It would be a major Coup for Marvel Studios to include Spider-Man in this movie since they are competing against Batman v Superman: Dawn of Justice and this would definitely "One-Up" DC on that front as far as Star Power in a movie. I have a separate article that deals with possible actors to play Spider-Man/Peter Parker, so I won't get into that here, but you can check it out- https://moviepilot.com/posts/2015/01/15/who-will-play-spidey-in-the-mcu-2588516?lt_source=external%2Cmanual%2Cmanual%2Cshare_fb&fb_ref=Default
So there you have it. Those are my choices for Heroes that Marvel Studios should add to the upcoming Captain America 3: Civil War movie. I didn't add Iron-Fist because his series is the last to film on Netflix (Fall 2016?) but he may be available for some other upcoming movie. We know he will definitely be in the Defenders series when it comes out on Netflix.
As far as Captain America: Civil War, I think with the available heroes and with the Russo Brothers adapting it to the big screen- It will work.