As it looks, to me, currently, Cyborg is in the Justice League (and has been set up as always being a member) and is not in Young Justice or the Teen Titans comics. And in the comics they have set up that it just started so its always been Red Robin, Superboy, Wonder Girl (not Donna), Kid Flash (Bart), and three others I do not know.
It would make sense to put their most popular characters into the movie, like Dick Grayson as Nightwing and Cyborg, but it also makes sense to follow the comic more so that fans wont go out looking for a comic and get confused. Why put characters into the movie who aren't in the current comic?
It will probably end up being like the Avengers or X-Men, where it sort of follows the comics but has its own continuity separate from the comics and cartoons. So we could see a mix and mash of characters. But I still think we wont get Cyborg, but he could end up in the Justice league movies instead of Martian Manhunter (who is going to be in the new JLA comic, so he could still end up in the movie too.)
Donna Troy however is not in the comics and not in the cartoon, if she doesn't show up in the next few years (like say they start making it in two years, and she isn't in anything) they might not use her because she has been absent for too long from any medium.
Wally is Kid Flash in Young Justice but doesn't exist in the comics anymore. So he might not get used because of that. Raven hasn't shown up either has she in the New 52?
What if the line up was
Tim Drake as Red Robin,
Super Boy (clone),
Kid Flash (Bart),
Aqualad (from the cartoon),
Wonder Girl (Cassie),
Artemis (cartoon),
Does the JLA movie need to come out first? For this film to make sense? What if they do this film but are unable to show any characters like Batman or Superman? Will this film suffer?