The cast for James Gunn's Superman: Legacy was just starting to round out before the SAG-AFTA strike put the project on hold. Per the actor guild's strike rules, actors are not allowed to negotiate future projects.
The strike came at a time when it seemed that we were just days away from finding out who would play Lex Luthor in Superman's latest reboot. It's also likely that we would have had more DC Comics superheroes join the cast as well.
In fact, finding out one more hero would have likely been a clear indicator of what superhero team will appear in the film.
The biggest clue that Gunn has revealed so far about the film is that it's set during Clark's early years at the planet. However, it's likely that not only will we see Clark Kent starting out as the low-man on the totem pole at the Daily Planet, but we' might also see Superman starting out as the rookie member on an already established superhero team.
Out of the hundreds of DC Comics superhero teams that exist, the recent revelation that Hawkgirl (Isabela Merced), Metamorpho (Anthony Carrigan), Mister Terrific (Edi Gathegi), and Green Lantern Guy Gardner (Nathan Fillion) will appear in the film severely cuts down on the number of potential superhero teams that could appear in the film.)
Click the Next button below to see which teams are likely to appear.
THE TERRIFICS
The Terrifics are a Fantastic Four pastiche from DC Comics, whose members are comprised of Mister Terrific, Metamorpho, Phantom Girl, and Plastic Man. As the most recently created superhero team that fits the selection criteria for possibly appearing in Superman: Legacy, most DC Comics fans immediately speculated that The Terrifics could potentially appear in the film.
The team came together in The Terrifics #1 (April, 2018) with the goal of exploring the Dark Multiverse- the shadow realm under the traditional DC Comics Multiverse. While it's unlikely that Gun would introduce the concept of the Dark Multiverse so soon, the introduction of the team would certainly plant the seeds for future use down the road.
Likelihood of Appearing: Medium
JUSTICE LEAGUE INTERNATIONAL
The revelation that Guy Gardner will appear in the film is a pretty strong clue that Justice League International might make their big screen debut in Superman: Legacy. Given the rich histories of other Lanterns such as Hal Jordan, John Stewart and Kyle Rayner, the only compelling reason to skip past them and immediately introduce Gardner would be for the JLI.
Guy is arguably the team's most famous member (outside of Blue Beetle and Booster Gold). However, Hawkgirl and Metamorpho have also been members of the team, at various points.
Likelihood of Appearing: Strong
THE JUSTICE LEAGUE
This would be the easiest team to introduce in Superman: Legacy, as almost every DC Superhero has been a member of the Justice League at some point (including the four heroes confirmed to appear). It would actually be somewhat humorous to see Superman shooting the breeze around the water cooler at the Dail Plant and at the Hall of Justice.
The lone drawback to the Justice League's appearance is that it sets the expectation that the team's A-listers will also appear: Wonder Woman, Aquaman, The Flash, and Batman. Given the disaster that was the team's last theatrical outing, DC Studios may opt to let a little more time pass before bringing these heroes back to the big screen.
Likelihood of Appearing: Very Strong
ALL THREE TEAMS
It's possible that Gunn and DC Studios may blow the doors wide open in the first film and introduce all three superhero teams. It's already confirmed that when audiences are introduced to David Corenswet's Superman, he'll be joining a world where superheroes have already existed for quite some time.
It would be completely in line with Gunn's comedic style to see all three of these teams in the middle of some world-saving mission, only for Superman to swoop in and effortlessly save the day before jaunting back to the Daily Planet. We could also see a competition between all three teams to recruit the Man of Steel.
Likelihood of Appearing: Low