How about Firestorm? If WB/DC can get a Firestorm character/film in the works quickly, then that might just be able to hold one over the MCU's Human Torch, providing the film is a hit of course. I know the character played a part on the CW, but there was a lot more potential with him, and the CW didn't quite do the character justice in my eyes.
Failing that, how about Vixen or Swamp Thing? The MCU hasn't quite got a character like that (yet?); there's a lot of characters I'd like to see from WB/DC, but there's already a Marvel counterpart to them. Atom has Ant Man, Doctor Fate has Doctor Strange, Green Arrow has Hawkeye etc
I could see Deathstroke as an over-the-top action fest like John Wick or Atomic Blonde. Nothing too expensive to make, but solid set pieces intercut with excellent fight choreography.
I'd totally be on board for this. It's a shame Joe(?) never got to showcase as Slade Wilson (although maybe, with the Snyder Cut, there's hope for him yet?)
From the given list of candidates, Hawkman should be seen as the next DC superhero to hit the big screen. I root for him.
Outside of the list, it's Green Arrow for me.
Green Arrow is a good call, but I'd prefer a film focused on both Green Arrow AND the Black Canary (they may need to overlook that Birds of Prey film or this though).
Hawkman I'm sure is great, but I'd prefer to see Hawkgirl first. Wonder Woman has proved that there's powerful women out there, and yet all of these big screen adaptions are men. Lets throw some female heroes into the mix, and whilst we're at it, launch a Green Lantern trilogy with Jessica Cruz (rather than Hal Jordan).