The actors confirmed at this point are Ryan Potter as Hiro Yamada, Jamie Chung as Yo Yo Tomago, Scott Adsit as Baymax, Genesis Rodriguez as Honey Lemon, and Khary Payton as Wasabi No-Ginger. While you may remember that Wasabi No-Ginger was portrayed by Daymon Wayans Jr. in the Big Hero 6 movie, Khary Payton has recently taken over the role in Big Hero 6: The Series, a TV show on the Disney Channel.
It's always so odd to hear a character you're familiar with speak with a different voice than you remember. So it's great to see most of the important Big Hero 6 characters taking up their roles in Kingdom Hearts III.
Notably, TJ Miller's Fred will not be showing up in Kingdom Hearts III, mainly because he's quite expensive. James Cromwell is an unknown at this point, so stay tuned.