You can't. The leadership roles are chosen seemingly at random and you can't determine this until you are in-game and looking at the character's bio.
However you can see them in your legacy pool, just not for the raw recruits as Sanges stated.
Mainly it’s random but if the character has law as their special most of the time they are sheriff or warlord. Those are the most experiences I’ve had. I could be wrong but you should try for yourself
What do you think?