According to Variety, the capacity of Cyborg in the film is unknown, so it's possible the appearance could only be a cameo.
Fisher's Cyborg first appeared in a small portion of "Batman v Superman" that signalled presence of other meta-humans on Earth, and the eventual formation of the Justice League. The character is set to star in his own film, currently slated for 2020. Miller's Flash, who also showed up in "Batman v Superman," appeared very briefly in a cameo opposite Jai Courtney's Captain Boomerang in "Suicide Squad."
Directed by "Dope" helmer Rick Famuyiwa, "The Flash" races into theaters on March 16, 2018.