The Marvel Cinematic Universe is about to break wide open in Doctor Strange in the Multiverse of Madness. Directed by Sam Raimi.
As Disney acquired the rights to 20th Century Fox movies. This has opened up many doors to bring in characters from the Fox-verse such as X-Men and Fantastic Four. The teaser trailer also hints at this by using multiple signature Marvel logos from previous movies.
Which characters are rumoured to be in Doctor Strange in the Multiverse of Madness?
Professor X

During sometime in August 2021, Pre-visual leaks revealed that Professor X would be joining The Illuminati. The leaks were showing that Charles Xavier will be going up against Wanda and holding Doctor Strange captive. Alleged Marvel insider MyTimeToShineHello has also confirmed this. Will this be a recast, Patrick Stewart or James McAvoy?
Magneto

If Magneto does show up, They’ll likely try to make it a personal fight, by maybe having this variant that looks like her father from that Earth fight Wanda/Scarlet Witch. Will Magneto be played by Ian McKellen, Michael Fassbender or recast?
Mister Fantastic

A person who claims to be a Marvel insider stated that Mister Fantastic has also been added as a member of The Illuminati. Will Disney completely recast or choose out of these two actors Ioan Gruffudd and Miles Teller?
Iron Man variant

As Tom Cruise was once considered as runner up for Iron Man originally, many fans think that an alternate Iron Man could arrive played by some actor other than Robert Downey Jr (maybe Cruise), as part of The Illuminati group to take on Wanda. Who else would you see cast in the role?
Black Bolt

The last live-action appearance of Black Bolt was in a poorly recieved show called Inhumans starring Anson Mount. A Marvel Insider stated that “Black Bolt was an idea early on not sure if he’s in the film”.
Captain Carter

Haley Atwell is rumoured to be returning, this time as Captain Carter scooped by insider ViewerAnon, this is more of a live-action reprisal from the animated Disney Plus series What If…? And she is a variant of Peggy Carter from the Captain America movies.
There will no doubt be so many more characters rumoured and confirmed in the near-future for this movie. Who would you like to see show up?