This Deathstroke series is said to be in the same vein as Vixen and The Ray, which are the other animated shows that have been developed for The CW Seed. Those shows used actors that also played the live-action versions of the characters in the CW series.
Deathstroke has played a part in The CW’s Arrow, Justice League, Teen Titans GO! to the Movies, and was most recently introduced in the DC Universe series Titans. There’s no information on who will be voicing the characters in the series.