The most likely WW3 conflict? Assuming the world goes broke(else no war possible sorry), then its
China(+US support) vs Russia(+EU support)
-China(workers demand more money, resource rich Siberia is a great way to get money)
-USA(forced to help China to maintain its own stability)
-Russia(possession of ressources)
-Europe(couldnt reach Siberia anyway, but has currently access via Russia).
Result: China gets glassed(never fight a war in Asia). But so will be many major cities. Not the first time this scenario is happening. But it always ends the same.