I'm friends with a scriptwriter on Justice League, He got fired for leaking this out, so fuck them. Here you guys go: The Film begins with Steppenwolf and Darkseid talking about Lex Luthor and the mother boxes being scattered over, Earth, Krypton, Atlantis and Themiscrya
Batman since the death of Superman has been devoted to becoming a superhero again, moved by Superman' sacrifice, And teams up with Wonder Woman to find Metahumans, In the event a threat from other planets and galaxies come.
Barry Allen, is a forensic scientist, obsessed with the murder of his mother, trying to find her killer. He has been Flash for 4 years, at this point. And is well known across Central City
Victor Stone, a former football player. When he visits his parents at work at S.T.A.R. Labs, an experiment with an inter-dimensional portal goes horribly wrong and a parademon kills Elinore. The creature turns on Victor and severely mutilates him before Silas forces the creature back through the portal. Leaving a Boomtube, As evidenced in BVS. He is mended with tech from Apokolips.
Arthur Curry, Son of a human man and Atlantian
mother, Helps out poor villagers with fish and other food, when Bruce Wayne, finds him and recruits him, to The League. Aquaman refuses at first. [/spoilers]