It's rather ironic that Gustin's most famous role to date is on a comic book show because the actor is rather familiar with comic books. He happens to be a lifelong fan of Superman and when he was a child, he would colour in pictures of the Man of Steel that his mother drew for him. As a result, he has a tattoo on his left arm that reads "Superman... I love him" and it's even written in his mother's handwriting.
While The CW does have a Superman in Tyler Hoechlin, Gustin has yet to share a scene with him. However, he does show up semi-regularly on sister show Supergirl, as the Scarlet Speedster is very good friends the Girl of Steel. Moreover, the musical crossover between the two shows even alluded to the fact that The Flash and Superman had met before, as Barry, through song, proclaimed that he wasn't impressed by Kara's "more famous cousin". Let's hope a meeting between the two takes place and Gustin gets to share the screen with his favourite superhero someday.