I know Hawkman and the new Cree girl will be joining after the first arc, but the team is still Adam Strange, the new Cree girl (based on Shannen Koostachin), Hawkman, Green Arrow, Animal Man, Martian Manhunter, Stargirl, and Supergirl, with Alanna Strange as a back-up.
I knew Catwoman would not be part of the team since she wants to be solo again. As for Katana, I could see her with the Birds of Prey. Vibe's probably going to be in the Flash family (I wish he could go to Earth-2 to stand toe to toe with Captain Steel; if you've read the comics in the 1980s, you'll get the reference). As for Simon Baz, I'm not too sure about what will happen to him, but I always wanted to see him in JLU since the team needs a Green Lantern. Maybe he can fill Hal's shoes in Justice League.
Here are some candidates for future members:
+Atom (either Ray or Ryan; he was my first choice ever since Hawkman and Green Arrow were announced; it could bring some nostaglia to the team)
+Black Canary (just to take Katana's place)
+Centrix (we really need the Global Guardians in the New 52)
+Booster Gold (he's Canadian)
+Blue Beetle (either Ted or Jaime)
+Captain Atom (this guy needs to make a comeback)
+Guy Gardner (if Baz is not available)
+Black Lightning (for diversity's sake)
+Metamorpho (with Silver Age favorites Adam Strange, Hawkman, Green Arrow, Animal Man, Martian Manhunter, and Supergirl on the team, now is the best time to put him in, too)
+Captain Steel (to take Vibe's place)
+Super Chief (same as Black Lightning)
Still, I'm super excited about Justice League United.