CAPTAIN MARVEL:
Actress: Lily James
Why her?: She is a very good actress, yet she isn't very recognized yet. She will star in this year's Cinderella and has done a perfect acting role in Downtown Abbey and Wrath of the Titans. (I am aware Emiy Blunt is perfect for the role, but she has been used in every Fan-Cast)
??Most noteable role: Korrina (Wrath of the Titans) or Ella (Disney's Cinderella)
Other character for her: Gwen Stacy
SPIDER-MAN:
Actor: Taron Egerton
Why him?: He is a young actor that according to critics has done an amazing performance in Kingsman: The Secret Service; He has also stated that his favorite superhero is Spider-Man.
Most noteable role: Gary Unwin (Kingsman: Secret Service)
Other character for him: Harry Osborn
BEN PARKER:
Actor: Michael Caine
Why him?: Outstanding actor, he has done an amazing work in every movie he appears in.
Most noteable role: Alfred Pennyworth (Nolan's Dark Knight Trilogy)
MADAME HYDRA:
Actress: Cate Blanchett
Why her?: She is a little old for the role, but her acting is outstanding and she has won 2 academy awards. She knows how to deliver a proper villain role.
Most noteable role: Galadriel (Lord of the Rings Saga)
ENCHANTRESS:
Actress: Yvonne Strahovski
Why her?: She is a fan-favorite for Captain Marvel and she will most likely get that role, but she is beautiful and has good acting skills to deliver a proper Enchantress, deadly but beautiful.
Most noteable role: Kate Morgan (24: Live another day)
NOTE: I'm not a native english, so please forgive any grammatical errors and please put them on the comments so I can correct them. Thank you.