JanghanHong
Enrico Trololo

This is what we do know:
Leader: Casimir III Wiki
Capital: Warsaw (as opposed to Krakow)
Color: Scarlet (background), Caput Mortuum (Lettering)
Symbol: Black Eagle (in perfect world, Austria and Poland would have each others' symbols)
UA: Solidarity (Free social policy upon entering an era)
UU: Winged Hussar, lancer replacement, said to fundamentally change the war combat is played. reliable source says that that it will push units backward, alluding to its heroic charge during the siege of Vienna.
UB: Ducal Stable, Stable replacement, 15 exp points to to mounted units, plus 1 gold bonus to pastures.
Secondary City-List:
Krakow
Wroclaw
Lods
Vilinus (currently Lithuania's capital, was a major city during Polish-Lithuanian Commonwealth)
The City list includes Vilinus, and the Winged Hussar is a lancer replacement, not knight. So it does seem to focus more on the Commonwealth rather than the period ruled over by Casimir III.