Not Chiang or Mao.
Definitely not Mao -- don't forget he was a member of the communist rebels trying to overthrow the Nationalist government at that time. Rebels don't get invited to victory parades
I don't think the American is Stilwell. Looks too young to be Stilwell... and also, Stilwell was relieved from his CBI duties in Oct 1944, later assigned to the latter stages of the Okinawa campaign in 1945. Because he no longer has "jurisdiction" in China, I don't think he would've gone back to Nanjing for a parade.