Today, the very first episode of Guess Who, "Revenge of the Swamp Monster" featuring Chris Paul, was released on the Boomerang app for free, even for those who don't have the service (I believe this is just a one-time thing that won't happen again with future episodes).
Additionally, on the show page on the Boomerang streaming service, a whole list of guest star silhouettes and air dates for the first season have been revealed. There are also 15 second clips from each episode posted (available to all, even if you don't have the service). Luckily for us, Boomerang did a pretty bad job in "hinting" at which guest stars will be in which episodes (it's essentially obvious between the videos, descriptions and silhouettes), so here's the entire list of guests that will be in the first season, in order:
Unfortunately, there are a few guest stars that were announced that will be in season 2, instead of season 1. These include Halsey, Bill Nye the Science Guy, Mark Hamill, Neil deGrasse Tyson, The Flash, and Whoopi Goldberg.