Okay, there's who should the MCU cast as these characters for 10 years of films and Disney+ series, and who is a good fit for the character as they are in the comics. They are two vastly different things. I'm going to do more of a lookbook sort of thing, just to capture the characters in theory.
Charlize Theron would be a perfect Emma Frost.
My girl Anok Yai proved she is indeed Ororo made flesh last Halloween.
Young Yul Brynner is Xavier.