Though Warner Bros. has had big success with its CW-based superhero shows, when it comes to the movies, the characters who are established on the small screen tend to be recast for the cinema. Ezra Miller, for example, plays The Flash in movies such as Justice League (while Grant Gustin is on TV). For Supergirl the small screen show, Melissa Benoist is the character. But as she enters the DCEU, Sasha Calle has the role and will first appear in The Flash.
Director Andy Muschietti confirmed the news on Instagram, including Calle learning that she's won the role in an emotional moment. The Flash will represent the first standalone adventure for Miller's Barry Allen, though "standalone" might be pushing it, since the movie will cross dimensions to feature Ben Affleck and Michael Keaton as their respective versions of Bruce Wayne/Batman.
The Flash has been in development for a while, chewing through different writers and directors, before settling on It filmmaker Muschietti, while Christina Hodson wrote the most recent draft of the script. It's currently scheduled to arrive in November 2022.