CallMeTheDoctor
Super Freak
I doubt a trailer will be shown before avengers more then likely it will be show at comic con and I suspect they will do a similar move like when marvel announced the avengers cast by having all the actors come out. I hope that green lantern is announced soon I can't see a justice League movie with out him in it.
Comic Con is a good location, but they would have so much exposure with AoU. Or they could even do a teaser trailer for AoU and then really blast off the trailer on amother day, and CC should get exclusive footage for something upcoming or maybe just announcements like you said.