The Marvel Cinematic Universe had humble beginnings with Iron Man. Each phase has upped the ante and stakes, building up to the climactic Endgame, but now it seems Marvel Studios is building towards a Multiverse Saga.
After the release of Spider-Man: No Way Home saw the return of several non-MCU characters, nothing's off the table. Disney's multi-billion dollar purchase of 21st Century Fox also gives them access to a slew of Marvel characters they could use. Doctor Strange in the Multiverse of Madness will further explore the reaches of the multiverse after fans were given just a small glimpse of it in Disney+'s What If...? series. The only question that remains is, who will show up?
Black Bolt (Inhumans)
While Inhumans was a huge critical and commercial flop, it did assemble a talented cast of actors. Although the show's canonicity remains unclear in the MCU, a simple explanation would be that it takes place in an alternate universe. So of course, it would seem plausible that one of them could appear in a film centered around the multiverse.
In the comics, Black Bolt is an integral member of the Illuminati, a secret organization that assesses threats and has been heavily hinted at in the trailer.
Captain Marvel (Maria Rambeau)
In the film's second trailer, a mysterious figure wearing a Captain Marvel costume is seen fighting Wanda Maximoff briefly. Many initially speculated this could be a variant of Monica Rambeau. However, that no longer seems to be the case. The short hairstyle this character sports is nearly identical to that of Lashana Lynch, who previously appeared as Monica's mother Maria in 2019's Captain Marvel.
Having Maria take on the mantle of Captain Marvel makes sense, as it's possible she comes from a universe where she was the one to test Mar-Vell's light-speed engine in Danvers' stead. While not much else is known, this variant will definitely give Wanda a run for her money in their fight.
Mr. Fantastic (2005 Fantastic Four Film Series)
While the critical reception for these films have been predominantly negative, fans have warmed up to them in recent years, with many praising Ioan Gruffudd's performance as Reed Richards. Mr. Fantastic is a staple in the comic book community and fans have been waiting for a faithful adaptation for a long time.
Although it'll be at least another year or two until the MCU Fantastic Four film comes out, Marvel is no stranger to introducing variant versions first after doing so with the returning villains in No Way Home and Patrick Stewart's return as Professor X in Multiverse of Madness. It shouldn't come as a surprise if he appears, as Reed Richards was famously a member of the Illuminati in the comics. Like Andrew Garfield was able to in No Way Home, Doctor Strange 2 could give Gruffudd the opportunity to flesh out his character further since he never got to finish his trilogy.
Loki (TVA)
The finale of Loki allowed the multiverse to be created after Sylvie killed the Kang variant, "He Who Remains". This allowed the villains in No Way Home to "squeak" through Strange's spell and for the heroes to traverse through the multiverse in Multiverse of Madness. Because of the multiple timelines converging, the TVA will have to get involved in the film at some point.
Last July, The Hollywood Reporter mentioned Tom Hiddleston was reprising his role from the series in the film and new information from IMDb suggests that he will appear alongside Mobius and Sylvie, as their stunt doubles were added to the crew of the film. Loki's role could be important, as only he and Sylvie know the truth behind the multiverse, information that can be vital to Doctor Strange.
Iron Man (Superior Iron Man)
Over the last few months, rumors have been swirling around that Tom Cruise could be playing a variant version of Iron Man, a meta-reference to the fact he almost played the role. Robert Downey Jr. received the perfect farewell in Endgame so it wouldn't feel right to have him return, but Loki and No Way Home have proved that variants don't have to look like their MCU counterparts.
The appearance of the Ultron bots in the second trailer definitely gives credence to this theory, as the MCU has established it was Tony Stark who created them. It would also just seem wrong not to have a version of Iron Man appear, as he was one of the founding members of the comics' Illuminati.
Spider-Man (Raimi Film Series)
Sam Raimi is back at the helm of a Marvel film with Doctor Strange 2 and with the recent appearance of Tobey Maguire's Spidey in No Way Home, it would be absurd not to have the director and actor reunite. It would also give the perfect opportunity to explore the Raimi Spider-Man world once more 15 years later.
Narratively and behind the scenes, this character makes a lot of sense to appear. Seeing Maguire's incarnation of the wall-crawler again will be just as amazing as it was in No Way Home.
Deadpool (X-Men Film Series)
Ryan Reynolds' portrayal as Deadpool has made the character an A-lister, with MCU fans clamoring for him to appear soon. The wait may not be much longer. The newest poster for Doctor Strange 2 features shards of glass with many different things on them and according to IGN, fans are now swearing they saw Deadpool in one of them.
Hot off the press for The Adam Project, Reynolds was asked about appearing in the new Doctor Strange film. His response was of course "no" but he seemed to be hiding something, similar to Andrew Garfield all last year. While Deadpool 3 is still a few years away, introducing him in a film featuring the multiverse makes the most logical sense.
Captain Hydra (Steve Rogers)
Even though Endgame gave an immaculate send-off to Cap, Chris Evans is way more likely to return in a future MCU project than Robert Downey Jr. would. Old Man Cap is still alive and obviously the multiverse contains countless versions of Rogers.
Interestingly, Chris Evans was reported to be finalizing a new deal with Marvel Studios last year by Deadline. However, he has yet to appear in any Phase Four project as of yet. A darker version of the character who is the complete opposite of his MCU counterpart would be a great way to spice things up.
Peggy Carter (Captain Carter)
Captain Carter emerged as a fan-favorite of the What If...? series thanks to a great story and the great voice performance Hayley Atwell gives. Even though her story in What If...? was largely a retelling of Captain America: The First Avenger, Multiverse of Madness gives the character an opportunity to grow and let the audience get to know her more.
Captain Carter can be an extremely integral part of Multiverse of Madness, as the film will feature Gargantos (renamed Shuma-Gorath due to rights issues), a multiversal being who seems to be after America Chavez and who Carter had previously fought in What If...? It also wouldn't be far-fetched if she turns out to be a member of the MCU's Illuminati, given all her experience in the Multiverse. Her appearance in the film is pretty much confirmed at this point, as her shield makes an appearance in the latest Strange poster.
Blade (1998 Film Series)
Wesley Snipes' Blade was the first major Marvel film to be released in theaters after previous attempts failed with Howard the Duck and Captain America. Blade featured some of the best action, spawned a franchise, and paved the way for the modern Superhero blockbuster. In short, Wesley Snipes' Blade is a legend.
Despite Marvel Studios moving along with a reboot starring Mahershala Ali, Snipes confirmed he had talks with Kevin Feige in 2015. Fascinatingly, another Marvel actor also revealed he had conversations with Feige in 2019. That happened to be Patrick Stewart, who of course ended up appearing as Professor X in the Super Bowl trailer for Doctor Strange 2. Wesley Snipes would be a welcome addition to the film and would definitely satisfy fans.