Unless we can train a governor..
All Empires (Sion) and Altar (Henchmen) can train "governors." When trained by a fortress with Command Post = +3 levels, so that's 5% (base champion) + 15% (Commander) + 10% (Administrator 1) + 10% (Administrator 2) = 40% Unrest reduction when just popped out of the unit factory. You can give them the "Veteran" trait for another +1, but it raises the wages and is generally overkill.
I generally make a unit called "Governor" just for this purpose for Empires/Altar. You don't expect them to be in any decisive battles, so you don't even need to equip them (though I usually give them a horse for mobility's sake.)