The problem being that, even if the US were to draft every last able-bodied men AND women between 18 and 49 they can get their hand on (which would be economic suicide)...
That's still just over one-third of what China can get drafting *only* the men.
Essentialy, it doesn't matter how much recruiting the US do - China can outnumber them easily.
As for the overall topic - who would win in a US-China conflict entirely depend on the war aims.
A direct confrontation (ie, direct Chinesse attack on US or the other way around) is extremely unlikely, if not downright impossible. In either case, if such a conflict happeened, the invader would lose - China has the manpower to invade but not the navy, and America has the navy to put an invasion force in China, but never the numbers to succesfuly invade.
The possible flashpoints for a China-USA conflict are pretty much limited to two of them - South Korea (highly unlikely) and Taiwan (a lot more likely). The Paracels/Spratleys, strategic or not, is not something the US will get their kids killed over.
If the conflict is over South Korea, then the advantage goes to China, who have no need of navy, and thus has a very easy time bringing their manpower advantage to bear, whereas American naval and aerial superiority, while still strong, isn't nearly as useful as it could be.
If the conflict is over Taiwan, then the US have the advantage, provided they can bring their navy to bear soon enough to deny China the crossing of the straits. As long as the USN can control that body of water, China's numbers are never going to be of any use, as they won't be able to put them on the battlefields.
