I'm not claiming to have any inside info, these are just my wild guesses bases on the evidence available to everyone.
The Flash Season 3.
1. I think we'll learn that on Earth-Three where JWS is Jay Garrick, that Dinah Drake, Laurel and Sara's mother from Arrow, is The Black Canary.
2. I think at the end of season 3 Barry Allen will "die", and Wally West will take over as The Flash. I think WB will want that so while their featuring Ezra Miller's Barry Allen in two movies that will come out during season 4 the TV Flash will be different. But regardless I think that would be a good move, because that's part of the Comics history of The Flash. Obviously a door will kept open for Barry to return, perhaps in the 100th Episode in the middle of Season 5.
1. The woman with the weird face in the trailer is Paula Van Gunther.
2. Bookend scenes set in the present will revolve around Diana talking to Carol Ferris (Christina Wren), where reference to Hal Jordan disappearing might be made.
1. Superman will return in about the middle of the film, but he'll instantly assume leadership, not unlike in Reign of The Supermen.
2. Green Lantern will show up at the very end, with maybe hints of his existence being made earlier.
3. Deathstroke will be in Justice League, he's who Batman will fight while the Superpowered characters fight aliens form Apokolips. That's what the footage we saw is from.
4. Enchantress will appear, that's why Bruce also got her file also at the end of Suicide Squad.
5. We'll learn the father of Eisenberg's Luthor is still alive, but probably not see him yet.
1. Zendaya is Michelle Gonzalez and/or White Tiger, not Mary Jane.
2. They will wait till he's in Collage to have him meet Gwen or MJ. What I want to see when we get there is Gwen and MJ being friends.
The Flash movie
Will flop and not get a sequel
Will be a hit and get a sequel
1. The first movie will be a version of Under The Red Hood with Arkham Knight influence. Harley and Joker will both appear. Mat Damon will play a villain replacing Black Mask's role, maybe Hush, and he'll hire Deathstroke.
2. Then in the second Justice League movie. Bruce will be "killed" by the Omega Sanction and the next Batfleck film will be Battle for The Cowl with aspects of Knightfall.
Update: The Official Deathstroke announcement came out right after I posted this. It kinda doesn't change anything, we know he'll be in Batfleck now, but I hope he's not the main or only villain.