Answer: X-Men 1 and 2 are canon. 3 is loosely canon with some changes.
Question: Is the MCU canon?
Answer: It isn't. However you may notice those versions of the characters in this game. Just the events are not canon.
Question: Can I play a child/relative of a canon?
Answer: Sure. You just need to ask the player(s) of that canons permission first and they will also have a say in your bio.
Question: Are any Characters banned?
Answer: The following are and the list could grow.
Manuel de la Rocha/Empath