If Snyder has already confirmed that Cyborg will make an appearance, then I think it's reasonable to believe that Ray Fisher is playing Cyborg. Ray fisher isn't a super popular movie star and back in febuary there was rumors that Zack Snyder met with
Michael B Jordan for a role in the movie, it was described as "Zack Snyder is currently looking for a black actor in his 20′s who is physically fit. It will be a small role in Batman vs. Superman, but the character will show up in future movies too". The Cyborg announcement wasn't made by Warner Brothers but it was also believable because the actor that was announced to play the role is some one that not that many people know who he is and he also fits the description about Zack looking for actors that are in their 20's and are physically fit.