Comic Book Writer Geoff Johns once said in a interview that he wants to write a movie script for The Flash or Superman and he did write a the Smallville TV Show Episode Legion if he were to write a movie script for a DC Comics Movies I think there are 4 key DC Comics Superhero Character that he should write a movie script for on my list below.
Producers=Christopher Nolan, David S. Goyer and Zack Snyder Director=Zack Snyder Writer=Christopher Nolan, Jonathan Nolan and David S. Goyer Batman (Bruce Wayne)=Christian Bale Superman (Clark Kent)=Tom Welling Wonder Woman (Princess Diana)=Jessica Biel The Flash (Barry Allen)=Damian Lewis The Flash (Wally West)=Zachary Levi Green Lantern (Hal Jordan)=Ryan Reynolds Green Lantern (John Stewart)=Sterling K. Brown Green Arrow (Oliver Queen)=Justin Hartley Black Canary (Dinah Laurel Lance)=Alaina Huffman The Martian Manhunter (J'onn J'onzz)=Phil Morris Supergirl (Kara Kent)=Laura Vandervoort Aquaman (Arthur Curry)=Kevin McKidd
Brandon Routh is another ok choice for Superman because he did a good job in Superman Returns.
The Smallville TV Show Justice League Team should be apart of the movie except for Impulse (Bart Allen) and Cyborg (Victor Stone) they should be in the Teen Titans Movie.
Use the Smallville Actors who have played Justice League of America members.
DC Comics Movies should do crossover like Marvel Comics Movies are doing and they will work with all characters including Nolan's Batman Universe it just needs to be well written and done right.
The Villians should be either Darkseid, Brainiac, Doomsday, and The White Martians.
The Comic Book Source Material should be Justice League of America: Year One mainly but other important story arcs and volumes should be used as well.