First, casting choices.
SUPERMAN:
Henry Cavill, obviously.
BATMAN:
Michael Fassbender would make a great batman, though I think they should keep Nolans Batman and Christian Bale. So if it is up to me, I stick with Bale.
GREEN LANTERN:
Assuming you want Hal Jordan, Ryan Reynolds was fine as GL, it is not his fault the script sucked donkey dick. No need to reboot it, just get a new director, and make Sinestro the villain in the second, with Mark Strong still as Sinestro. If you want to take a risk and go Jon Stewart, Chadwick Boseman seems the hot choice, but I prefer Nate Parker. FWIW I think Hal Jordan is a better choice, and it gives you the oppurtunity to have him turn into Paralax as a villain for a Justice League Sequal.
FLASH:
Jake Gyllenhaal would be good as Barry Allen, if they go Wally West, I would Suggest Bradley Cooper. But since I prefer Barry Allen, im going to stick with Gyllenhaal. Hes funny when he needs to be, and he has fantastic range.
WONDER WOMAN:
I would go either Gina Carano or Jamie Alexander. But since Jamie Alexander is already Siff, Carano gets the edge here. She is relatively new to the scene, and we know she can pull of the action scenes. She is sexy, and she kicks ass, nough said. Wonder Woman is probably going to be the weak link in this Universe, so it MUST be cast well.
MARTIAN MANHUNTER:
Benedict Cumberbatch is my choice here. Fantastic acting talent, perfect voice for J'onn J'onnz, and he looks just like him for christs sake. Cumberbatch is the best new actor in hollywood, and is the only person who can pull off this character IMO.
AQUAMAN:
Now personally, I do not believe they should use Aquaman, I think he is cheesy, and probably would be hard to make work on the big screen. That being said, if I had to choose one guy, I would go with Liam Hemsworth. He has been great in everything I have seen him in, and I think he has the presence to pull of the King of the ocean. Personally I dont think Aquaman should be used however
CYBORG:
An interesting character, who could be introduced as someone akin to Hawkeye or Black Widow in the marvel universe. He doesnt need his own movie, and could appear in any one of the other films. For him, I would chose Chadwick Boseman. Nice up and comer, was great in 42, give him a shot and he could get his own spin off.
GREEN ARROW:
Again Doesnt need his own film, even though I would like to see one. He is a very cool character, that is basically a hybrid of Tony Stark/Ironman and Bruce Wayne/Batman. He would be a pretty tough cast IMO, but one person does come to mind when I think of Oliver Queen. That is Charlie Hunam. I am a big Sons of Anarchy Fan, and I must say, Charlie is a fantastic actor. He has great screen presence and great range. Ive seen him play a bad ass biker, a soccer hooligan, and he looks great in the upcoming Pacific Rim film.
VILLAIN:
And who should be the villain? I think you could go many directions with this. I think Darkseid, as much as I would absolutely LOVE to see him in this film, would be too much too soon. I think he would be best served in a Justice League sequel. He is the ultimate enemy of The Justice League, and should be their final foe. Now, if you only plan on making one, then by all means use him, but I dont think that is what they are trying to do. In any event, they must use Darkseid eventually, and it doesnt really matter who plays him physically, since he will be mostly CGI, so whether they wait until the sequel or use him in the first one, I would cast: Christopher Lee
What about The White Martians? They could be a good choice, but I think that could be too similar to the Chitauri from The Avengers if done wrong. If you are DC, you dont want this to come off as a rip off of the Avengers, so if they go this direction, they have to be careful to portray them the right way. Also, if they go this direction, it could be a great way to introduce The Martian Manhunter, without having to give him his own movie. You could have Lex Luthor bring them to earth, or something like that. Lex Luthor could be played by Hugo Weaving, or perhaps my wild card and choice for this role: Idris Elba
And what about Vandal Savage? I think this could be the perfect choice. Vandall Savage is a Great Villain, and could potentially bring together villains from the other movies in the franchise together to face The Justice League. For Example, he could recruit Sinestro, Professor Zoom, Bane, (barely surviving the events of TDKR), Metallo/Brainiac/Atomic Skull (really whoever they go with in MOS2), Cheetah, and Malifa'ak. You can see this is starting to look somewhat similar to Justice League Doom, which was a great animated film, and I think could be a great plan for a come together Justice League Movie. Vandall Savage could be portrayed well by Jason Isaacs.
Of those 3 choices, I would go the White Martian route first. I think it provides a great reason for the, all to come together, and could help introduce new characters. Then, I would follow with Darkseid for the second and final JLA film. However, all three would work well.
Now with all that being said, here is the list of films I believe should constitute the DC Cinematic Universe Films, by year with the villains for each film as well. For the Purposes of this discussion, first I am going to assume there is only one phase, although I do not think that is actually the case. After that will be a list of films in a universe with more than one phase.
One Phase
1. Dark Knight Trilogy (2005-2012)
2. Green Lantern (2011)
3. Man of Steel (2013) Villain: Zod
4. Flash (2015) Villain: Zoom
5. Green Lantern 2 (2015)Villain: Sinestro
6. Wonder Woman (2016) Villain: Cheetah
7. Man of Steel 2 (2016) Villain: Brainiac and Lex Luthor
8. Justice League (2017) Villain: Darkseid
Two Phases
1. Dark Knight Trilogy (2005-2012)
2. Green Lantern (2011)
3. Man of Steel (2013) Villain: Zod
4. Flash (2015) Villain: Mirror Master or Gorilla Grodd
5. Wonder Woman (2015) Villain: Cheetah
6. Man of Steel 2 (2016) Villain: Brainiac
7. Justice League (2017) Villain: The White Martians and Lex Luthor (Darkseid after credits)
8. Green lantern 2 (2018) Villain: Sinestro (Flash after credits)
9. Flash 2 (2019) Villain: Zoom (Batman after credits)
10. Batman 4 (2018) Villain: The Riddler and Deadshot (Superman after credits)
11. Man of Steel 3 (2019) Villain: Doomsday & Lex Luthor (Batman, Superman, and Amanda Waller after credits talking about Darkseid's impending arrival)
12. Justice League 2 (2020) Villain: Darkseid