How The Flash Will Solve DC's Batman Problem
Batman Returns
We know that Michael Keaton will appear in The Flash as a veteran Batman. Whether or not he's the exact same one we saw in the '89 film and Batman Returns remains to be seen, but none of that explains how he now exists in the DCEU. Well, the answer may be simple: He doesn't. Or at least not yet.
The story of Flashpoint is as follows: Barry Allen decides to go back in time to save his mother and, by doing so, creates an offshoot timeline in which he never became The Flash, multiple heroes are different (i.e. worse) and there's a huge war being waged between the Amazons and the Atlanteans.
As for how the movie does that remains to be seen, but if they do end up using time travel, or somehow use it as a portal into the multiverse (as the theories suggest), that would explain how Barry ends up crossing paths with this Batman when the two of them don't exist in the same universe.
On a side note if this is the '89 Batman, The Flash could very well end up making DC's entire library of films and TV shows canon to its cinematic multiverse - just as the Arrowverse did on TV. And if they do it on-screen - and explain it well - it should allow viewers to at least begin to understand why there are so many Batmans.
But with new beginnings comes an ending...
Cont.