Of course, at the moment, war with Russia wouldn't make sense since China is not yet fully independently making their own military equipment. The probability of attacking your number 1 supplier for fighter engines, tanks and other such things ... well its not likely.
I very much doubt that Russia would have any hope of winning such a war, but I think their enormous Cold-War buildup of weapons would help a great deal in the initial phases. Once they run out of all that, they're doomed. China can currently outproduce any nation other than the US and Japan. Russia's a good ways down the list for output these days. The former Soviet Union vs China would have been a MUCH more interesting fight.