Grant Gustin gave a whopping nine years of his life to the CW's version of The Flash. Starting in 2014 and running all the way until 2023, the show might not have had the best effects, writing, or anything really, but fans stuck by it, probably hoping Grant Gustin would get to upgrade his costume at some point.
Sadly, even after putting in one hell of a shift as The Flash, Gustin was replaced in the DCU movies by Ezra Miller. However, when asked while doing a signing for fans about whether he'd be up for a return, Gustin said that he trusts James Gunn.
There seems to be a lot of people who share that sentiment among superhero fans, but the jury's still out on whether Gustin will make his return. It did seem like Ezra Miller had impressed with their performance in The Flash movie, so we'll have to see what's next for dear old Barry Allen.