In case you haven't heard the big news, Robert Downey Jr. is reportedly close to signing on for "Captain America 3," to kick-start the Marvel Cinematic Universe's version of "Civil War," the comic book story arc that sees Tony Stark and Steve Rogers squaring off over the legality of the Superhuman Registration Act — a law that forces superheroes to unmask and register with the United States government.

Iron Man's inclusion in the third (and final?) "Captain America" movie is a very big deal for some very obvious reasons, not the least of which is that it essentially gives us a bonus "Avengers" movie just one year after "Avengers: Age of Ultron." Not that we can expect to see every single hero of the MCU appear in "Civil War," but the fallout of Cap vs. Stark will surely be felt throughout the next several Marvel movies.

Which side will Earth's many mighty heroes take in the escalating conflict between Iron Man and Cap? Here's what we think:

Black Widow

Smart money says she's with Steve, considering their friendship and working relationship in "Winter Soldier." Then again, Natasha has a relationship with Tony Stark as well, dating as far back as "Iron Man 2." On top of that, in the "Civil War" comics, Widow throws her hat in with the pro-registration lot. Perhaps her vote is more up for grabs than one might think.

Hawkeye

Wherever Natasha goes, he goes. If Widow wants in with Cap, Hawkeye wants in with Cap. If she wants in with Stark, he wants in with Stark.

Thor

He isn't likely to have a dog in the fight, as he'll have his hands full dealing with apocalyptic shenanigans at home in Asgard, thanks to Loki ruling over the kingdom, posing as Odin.

Hulk

Bruce Banner doesn't seem like the type of guy who wants to answer to anybody, as far as his powers as the Hulk are concerned. But he's also great friends with Tony Stark; does that friendship transcend Banner's need for privacy? Maybe he won't have to choose; after all, rumors suggest that Hulk will have some off-world problems of his own after "Age of Ultron."

Quicksilver and the Scarlet Witch

We won't know anything about how these characters function within the Marvel Cinematic Universe until after "Age of Ultron," so it's just too soon to say. In the comics, Scarlet Witch is uninvolved in the conflict, while Quicksilver sides with Cap. Could we see a similar outcome on the big-screen?

Vision

See above; we just don't know enough about the MCU's Vision to make a call. The character was deceased at the time of the "Civil War" event in Marvel Comics, so his loyalties are up for grabs in the movie version.

Nick Fury

Cap all the way. No chance Fury supports the government, not after the great S.H.I.E.L.D. conspiracy.

Maria Hill

Stark all the way. She's employed by Stark Industries by the end of "Winter Soldier," and she's a pivotal player on Iron Man's behalf in the "Civil War" comics.

Falcon

Conventional wisdom says Sam Wilson will fly with Steve Rogers wherever he wants to go. But in the "Civil War" comics, Falcon actually aligns with Iron Man. Sam choosing Stark's side of the line doesn't seem to make sense in the MCU, however, so this could be one way that the "Civil War" movie and comics diverge.

Sharon Carter

All about that Cap.

The Winter Soldier

He probably wants to keep a low-profile, given the whole "brainwashed Soviet assassin" thing he's got going on. With that in mind, and his past life's friendship with Rogers, expect to see Bucky Barnes siding with the First Avenger.

War Machine

Wherever Tony Stark goes, James Rhodes goes.

The Guardians of the Galaxy

No side. Bigger fish to fry.

Ant-Man

By the time we see "Captain America 3," both Scott Lang and Hank Pym will be established in the Marvel Cinematic Universe. As with Quicksilver, Scarlet Witch and Vision, however, it's too soon to say where they would fall. In the comics, Hank Pym sides with Tony Stark, but that doesn't really count, because at the time, Pym is secretly a Skrull. Lang, meanwhile, doesn't have a dog in the fight, because, well, he's dead. Sort of. It's complicated.

Doctor Strange

The "Doctor Strange" movie debuts in 2016 after "Captain America 3," so maybe, just maybe, we'll see the Sorcerer Supreme pop up here — or at least react to the fallout in his own movie. Keep in mind that Strange was name-checked in "Winter Soldier," so a role in the next "Captain America" isn't too far-fetched. As for his allegiance, Strange sides with Steve in the comics, so why not expect the same here?

Captain Marvel

Carol Danvers does not exist on the big-screen yet, but we're bound to see her before long. If her arc mirrors the character's role in the "Civil War" comics, then you can bank on Captain Marvel working side-by-side with Iron Man.

Black Panther

Again, not officially in the MCU just yet, but T'Challa's inclusion on the big-screen has to happen sooner or later. In the comics, he's on Team Cap.

Agent Coulson and the Agents of S.H.I.E.L.D.

Consider Coulson's trust issues with the government and his adoration for all things Captain America. Very safe bet that the remnants of S.H.I.E.L.D. want nothing to do with the Superhuman Registration Act.

Daredevil

Could we see Matt Murdock with a role in the "Civil War" movie? We'll have 13 episodes of his Netflix series under our belts by the time the new "Captain America" hits theaters. Daredevil has a brief but memorable role in the "Civil War" comics that many fans would love to see.

Spider-Man

Yeah, right. But maybe? Peter Parker plays a huge part in "Civil War," but he's not an accessible Marvel Studios character, thanks to Sony owning his big-screen rights. Then again, there have been rumblings of Sony and Marvel reaching an agreement over how to share Spider-Man. Could this be Peter Parker's coming-out party in the Marvel Cinematic Universe? It's a long shot, but it's not completely out of the realm of possibility — close, but not completely.

"Captain America 3" hits theaters on May 6, 2016.