Two good comedy actors is essential imo.
I think this movie's identity should basically be the next Goldberg/Apatow style comedy movie, but about superheroes (the same way Sausage Party is that for animated movies). The entire cast should be modern comedy actors like in This is the End. That's the way I can see it really turning heads. I say they should go R-rated for language too, like most comedy movies these days do.
For Booster: Zac Efron, James Franco, Dave Franco,
For Kord: Jake Johnson, Seth Rogen, Jason Segal, Jonah Hill, Jay Baruchel