I dont think a Red Dead movie will ever be made to be honest, VG adaptions have a rep for sucking, but if it was to happen, who would you like to see play who? For me ....
Arthur Morgan = Chris Pratt ( he would have to drop his cutesy shtick though )
Hosea Matthews = Daniel Day Lewis
Micah Bell = at first I was thinking Josh Holloway, but he is too handsome to be that rat, so I dont know.
Pearson = John Goodman
Dutch = I wanted DDL for this, but figured he may be a bit old to play Dutch as there would no doubt be gun fitghts and action in a Red Dead movie and Dutch would no doubt be at the forfront of it, thats why I changed him to Hosea
Lenny Summers = Justice Smith / John Boyega
Sadie Adler = Charliz Theron
I have not thought of any more yet, still thinking.