According to EW:
What we have seen remains faithful to the comic book that first appeared in 1960. All seven original members of the Justice League -- Batman, Superman, Wonder Woman, the Flash, Green Lantern, Aquaman, and the Martian Manhunter -- are featured in an origins story about the superhero conglomerate. The plot revolves around villainous businessman Maxwell Lord and involves cyborgs called OMACs (One-Man Army Corps), who can take over humans and turn them into killing machines. There are epic battles between Superman and Batman, as well as Superman and Wonder Woman.
EW also confirms that the character list includes Superman, Wonder Woman, the Martian Manhunter, Green Lantern (John Stewart, the same Lantern from the Justice League Animated Series), Batman, the Flash (Barry Allen) and Aquaman.
Long-time comic readers will quickly recognize that the plotline closely resembles that of the 'Countdown to Infinite Crisis' storyline from 2005-2006 in the pages of DC comics. It'll be interesting to see how they combine that storyline with an origin story about the formation of the team.