Background info: With the success of Avengers it only makes sense for DC to get their act together and capitalize on its success with their own group of super heroes the Justice League. The Superman,Batman and Green Lantern have already been established some better than others. However you could start a JLA film with a shared universe with those franchises and introduce Flash,Wonder Woman, Aqauman and Martian Manhunter into the film and then give them solo films after it. 3 out 5 audiences members who would see the film already have a general idea of who those characters are anyways.
Synopsis:
A global threat has emerged from the darkest depths of space the being known as Darkseid has set his eyes on Earth and wants to make its inhabitants his slaves and rule with an iron fist. However he did not expect to encounter the world's greatest Heroes the Justice League!
Superman:Henry Cavill
Henry is the latest actor to don the iconic cape and "S" symbol, I have seen is work on the Tudors and I can see the direction he will take the MOS. It is sure to be one of the more faithful interpretations of our time.
Batman:Jon Hamm
Bale is retiring after TDKR, and the series is going to be rebooted so Bats will be recasted for JLA. Jon Hamm is the ideal choice for an older and seasoned Batman. The JLA would be the right time to introduce him as Batman while the audience already knowing the characters back story/history.
Wonder Woman:Ginnifer Goodwin
I never saw any of her work until this year on Once Upon A Time. She has the right mix and look to play Diana, she can be the sweet princess as well as warrior all at the same time. I have never seen her cast for this role but I think she would do well with it.
Green Lantern:Nathan Fillion
Now I know I will get a lot of slack out of this but I think he should've been cast a few years ago in this role when the film was first announced. Nathan is Hal Jordon just listen to him in the animated movies. This Hal would also be an older and more skilled Green Lantern.
Flash:Neal Patrick Harris
He is the ultimate choice for Barry Allen aka the Flash. He has the right acting skils to bring him to life and knows when to be serious or funny. He would own the role if given the chance.
Martian Manhunter:Dennis Haysbert
Haysbert is a great choice for the Manhunters human form and could do the MO-Cap performance for the Manhunter without any trouble. He also has the perfect voice for him.
Villains-
Darkseid: Michael Ironside is perfect for Darkseid he could do the voice and body work as well by using the same techno. as the did for the hulk with Mark Ruffalo.
Granny Goodness:Kathy Bates
she is one of my favorite actresses of all time and now that she is getting older she would be the ideal choice for Granny.
The Furies-
Mad Harriet:Kristen Stewart
would be a different role for her and would be a challenge for her but I could see her pulling it off.
Lashina:Olivia Wilde
Olivia is an fan fav. for Lois Lane but I am going to cast her as Lashina, she is good with roles that have stunt work and this would be a good role for her to delve into.
Stompa:Gabourey Sidibe
Yes she is black however I don't see where that is a big concern, Marvel did the same thing with Idris Elba in Thor and he owned the role and was one of the better parts of Thor. She could do the same with Stompa.
Supporting Cast-
Lois Lane:Amy Adams
The next Lois Lane I think she will do well next to Henry Cavill as Superman.
Perry White:James Caan
The ultimate Perry White you'd know what I mean if you watch him in Misery and on Las Vegas.
Jimmy Olsen:Caleb Landry Jones
He looks just like Jimmy just put a camera in his hands and you have your Daily Planet photographer.
Alfred Pennyworth:John Cleese
He has always been and will continue to be my choice for Alfred DC needs to make this happen.
Jim Gordon:Bryan Cranston
He was great in the animated DC movie as the voice and I would love to see him in the live-action role. He is Jim Gordon just watch breaking bad.