In regards to the matter, here is what creator, Andrew Kreisberg, had to say,
“Greg, Ali and I are beyond thrilled to welcome Clark Kent and his slightly-more-famous alter ego to the world of Supergirl. Superman will be appearing in the first two episodes of the new season and we cannot wait to see who next dons the red cape!”
Now it’s time to open up the can of casting speculations. The number one name that comes to mind is Tom Welling. As many of you may or may not know, Welling took on the role of Clark Kent 15 years ago when a show called Smallville debuted on that exact same network. The series would go on for 10 seasons with Welling’s version of Kent finally taking on the mantle of Superman in it’s series finale. Interestingly enough, fans had to deal with the show’s motto “No flight. No tights” until the very end when the show rewarded it’s faithful audience with it all. In that story, Kent went from high schooler to college drop out (due to heroic responsibilities). He would then go on to work at the Daily Planet for several years before the show ended. Therefore, even with the show’s absence for half a decade, Welling’s version of Kent would fit just fine into the timeline of Supergirl.
So, if you can’t cast Welling, who can you cast? It definitely won’t be Dean Cain. He already plays her father on the show. In the end, the best thing to do would probably be to cast someone who is relatively unknown. It would provide a fresh beginning to this already young show, and that way you have nothing to compare it to.
Supergirl season 2 airs this fall on The CW.