China already has access to any natural resource they want in Siberia, they can simply buy it from a friendly seller, and they don't need it to house or feed their people. Japan will be the the Target of Chinese expansion (for good reason), then South Korea.
China won't touch Russia until China is Administering several Protectorates that USED TO BE US States, and the Philippines.
China will also make on move on Mongolia before Siberia.
Mongolia is a Russian ally. Many Mongolians speak Russian. But Russia has less incentive to defend Mongolia than Siberia. So it's a softer target for China.