Siberia is the logical choice because of the natural resources lying under the tundra, and there just aren't that many people there now. I don't think they'll make any pushes into Alaska as they have practically no amphibious capability(they still lack the means to invade Taiwan).
actually, it is a well known fact that russia is inviting chinese people to siberia to exploit it economically. siberia is well stocked with chinese companies and people. if im not mistaken, russia is also allowing china to buy large tracts of land in siberia.
Besides, Pushing into Alaska typically means the Aleutians.