Well, Snyder himself has now revealed that Justice League 3 would have essentially been Man of Steel 2, focusing very heavily on the arc of Henry Cavill’s Superman.
So, Justice League 3 would have played out like Man of Steel 2, completing Clark Kent’s arc which began back in 2013.
Like the final chapter [Justice League 3] was going to be a large percentage of Superman to just bookend the whole thing.
“And Superman basically is going to be the head of the Justice League and the Armies of Men.