A casting call website is stating George Miller is on board the Justice League movie as a producer, and also that Amber Heard has been cast as Mera.
Acting Audtions has a Justice League casting call listed for actors and extras where the movie has a working title of "Caveman." The credits list George Miller as a producer along with Charles Roven, Deborah Snyder, Doug Mitchell, Barry Osborn and Dan Lin. Executive producers stated are Wesley Coller and Geoff Johns, with the script by Chris Terrio.
The site even has a description of the Justice League movie as: "Earth’s greatest heroes are assembled to form the Justice League, to combat a threat beyond each member’s capabilities."
Miller, who was previously behind the defunct 2008 Justice League Mortal movie, was also rumored at one time to be directing a Man of Steel sequel and confirmed DC talks. Zack Snyder also left the door open for Miller to be involved in the DCCU.
Amber Heard has previously been rumored for Mera, Aquaman's love interest.
Justice League - Part 1 has a November 17, 2017 release; Zack Snyder is currently in pre-production and starts filming April 11th in the UK.
Snyder recently tweeted out the following image alongside Jason Momoa with the Justice League costumes teased in the background in additon to what is thought to be Mera concept art (to our left of Snyder).