I always thought that Isabelle Huppert
would have made a perfect Scarlet ... uhm, Sylvia. Maybe that pick will be a bit controversial, so imagine Ms. Huppert being slightly younger than she is presently.
Helen Mirren for Maggie is a good fit. So is Maggie Smith.
The portlier dude in all the bromedies is Parson, obviously.
Ansom could be played by Captain America, Draco could play Trem (and in an attempt to shed that one role, Daniel Radcliffe would play Jack ... if he wins the fight to the finish with Christian Bale first) and Queritch should play Ace. Stanley Tucci for Sizemore?
Al Pacino for Stanley. Hey makeup and a close shave can do everything.
The role of Wanda will be played by a blackface Robert Downey Jr. in drag. Nah I kid. Lucy Liu might fit the role maybe, though.
The whole point of this is lost if you keep it a secret.