To kick things off, we shall have the Justice League members.
Kal-El/Clark Kent - Brandon Routh
I would still involve him as he was great as Superman, could be both a battle hardened Superman and also a compassionate one which is what Superman is.
Bruce Wayne - Christian Bale
I think Christian is the best Batman ever apart from that voice, but that can easily be changed everything else is perfect.
Hal Jordan - Ryan Reynolds
Although this is yet to be released and we haven't seen Reynolds as Jordan, I firmyl believe that he would be great and would keep the solo movies connected in one big universe.
Diana Prince - Jessica Biel
Thinks she looks good, can act and is going to be huge after the success of the A-Team movie.
Wally West - Chris Pine
Did a great job as Captain James T Kirk and played a good humurous side of him, which reminded me a lot of Wally West. Would look good as Wally and has the acting skills.
J'onn J'onzz/John Jones - Djinson Honsou
It was a tough choice between Djinson and Laurence Fishbourne, with both would have been great at the job.
Orin/Arthur Curry - Phillip Winchester
This was by far the hardest to cast. I know very little about Aquaman from the comics other than his origin and name. So deciding what Aquaman to portray was tough.
Now for the villains in the movie.
Darkseid - Dwayne Johnson/Michael Duncan Clarke
Johnson would be in soe pretty heavey makeup mixed together with CGI, much like Eckhart was as Two-Face in TDK, with Clarke's voice, this doesn't get better.
Lex Luthor - Billy Zane
I know what users on here say about Zane, but if you watch Titanic, he plays the suave businessman very well, that is my Luthor to a tee and he is naturally bald.
Amanda Waller - Grace Jones
I would completely change Waller into a more muscular woman who has a past as a battle hardened soldier as apose to the fat pencil pusher, I think the audience would go for this more.
Kalibak - Glen Jacobs
This was a tough casting but I thought Jacobs would be able to play it good, has the growly voice, ugly and would be in heavy make up.
Granny Goodness - Judi Dench
She has shown in Casino Royale and QOS that she can portray a tough lady and would be a very good Granny Goodness although it would be a major role, more supporting.
Now for the supporting cast which involves background characters, cameos.
Lois Lane - Kate Beckinsale
Lois Lane needs to be a big actress who can carry the role, the pressure an also act. She looks good, beautiful and is a strong character.
Jimmy Olsen - Paul Dano
There isn't anyone better for the job
Perry White - Ed Harris
I believe would be great and would be like Freeman is to the Batman franchise to the Superman fanchise.
Kara Zor-El/Kara Kent - AnnaLynn McCord
Kara would be not be in the main JL but would be a background character protecting Metropolis whilst Superman is trying to save every city on the planet.
The characters that I haven't cast are listed below. This is because I don't have the time, know too little about them and will be in a future film and will already be cast and I would happy with that casting.
Suicide Squad
Green Lanterns
Thousands of Para-Demons