One of the rules of James Gunn's new DC Universe is that he doesn't plan to cast actors who have already appeared in his DC shows or movies as new characters. However, the filmmaker states he's willing to make certain exceptions - particularly for Chukwudi Iwuji, who portrayed Clemson Murn in Peacemaker season one.
Speaking on the official Peacemaker podcast (via ComicBook), Gunn says "I think Clemson Murn is canon… Maybe his face might not be canon if we want to cast Chuk as something else in the DCU. But also, Chuk could end up being some other character, maybe [one] that isn’t so humanoid."
