At the moment, there is no set project among DC's upcoming movies for The Flash to appear in, even though fans continue to ask for Arrowverse The Flash star Grant Gustin to play the DCU's Flash. However, the situation recently shifted for Wonder Woman, who now has a movie being written by Supergirl's Ana Nogueira, a priority for the DCU movie slate.

On Peacemaker The Official Podcast with James Gunn, the DC Universe's creative chief, Gunn, revealed that he does not know whether Wonder Woman and The Flash were canon to the franchise at the time of the events in Peacemaker season 1, episode 6.

In James Gunn's Superman, the movie begins with an opening crawl that establishes key information about the larger DCU and David Corenswet's version of Superman before diving into the Man of Steel's story. Superman has been active as a superhero for the past three years in the DCU, with others like the Justice Gang also operating in Gunn's DC Universe.

Given how The Flash and Wonder Woman are probably going to be around Superman's age, something Gunn has said will be true for Batman, then it means the heroes could have been active for the past three years of the DCU. However, that is not the only possible path for the characters to play a role in the franchise.