It would be cool if they get David Oyelowo as the live-action Agent Kallus. I mean, he looks good in black, can pull off the ISB Agent look and the sideburns/beard/whatever that thing is. Plus he has The Voice™, so he’s the perfect choice for me.

I guess live-action Zeb has to be all CGI, so I don’t have a preferred actor in mind, maybe someone very tall? XD
If they remember the hint/reference of Zeb in Battlefront II, Zeb should be fine, but since it’s not a direct one, so it’s not a hard evidence of him surviving, unlike Hera’s appearance in Force Destiny, so it’s hard to tell. But I don’t think they will kill of another main cast after Kanan, and thus Zeb is relatively safer. Kallus, on the other hand, is more or less not that safe. Him being not in the main cast, and the trope of former villain dies in the process of saving their new friend/the whole atonement thing… but I hope the show’s death quota is already filled, especially when they still have to sort out the whole Ezra being a known Jedi thing (I suspect Ezra won’t “die” but rather become one with the Force/Lothal), and the fact that they will most likely let Pryce instead of Thrawn bites it, there will be too much main cast casualty to let the side character die.
I know, I’m being optimistic…