Is not only about Casting, writer and director.
Is about storyline, inside jokes, movie concept art, filming locations, cameos, movie suits and more.
Characters that are not members on the comic but could be in the movie to gain Popularity boost.
Deathstroke the Terminator: Robert Patrick or Tim Roth or Stephen Lang or Hugh Laurie
Harley Quinn: Diora Baird or Kristen Bell or Kaley Cuoco or Amanda Bynes
Change Oracle for The Calculator, main reason she is a child in Batman Nolan Movies, also the Supervillian Team idea works better
The Calculator: Johnny Galecki or Michael Weston
Now Real Team Memebers
Deadshot: Christian Slater or James Marsters or Jason Statham or Jeffrey Dean Morgan or Wentworth Miller
Poison Ivy: Rachel Nichols or Krista Allen or Christina Hendricks
Bronze Tiger: Henry Simmons or Erik King
Amanda Waller: Angela Bassett (She is inside the Green "Deadpool" Lantern Movie)
Black Orchid: Summer Glau or Elisha Cuthbert or Olivia Wilde
Captain Boomerang (Digger Harkness): Mark Hamill or Ray Liotta
Captain Cold (Leonard Snart): William Shatner or Paul Giamatti
Count Vertigo: Zachary Quinto or Ralph Fiennes or Paul Bettany
Doctor Light (Arthur Light): Michael Emerson or Robert Knepper
Enchantress: Rhona Mitra or Jodi Lyn O'Keefe
Nightshade: Emily Blunt or Karen Cliche
Vixen: Meagan Good or Kerry Washington
Rick Flagg, Jr.: Christopher Meloni or Thomas Gibson
Deadstroke?: Ryan Reynolds (Just a joke)
Director: Lexi Alexander or John Woo
Martial Arts Choreographer
Gun Kata Choreographer Jim Vickers
This is all what i have to this point.