If you don't count the US' national guard units you can't count the Chinese reserve units....
Also, do the Chinese run similar theories to the Norks where EVERY citizen is considered to be in the reserve army? If so, wow, 1 Billion, give or take, combatants against the US... that'd suck big ones.
Also, I would hazard a guess that neither the US nor China will want to invade the other for fear of nuclear retaliation or just fear of a meat grinder.. it'd probably be played out in some third world country or theatre that is not close to home (Middle East, Africa, Pacific)