It's Canada! duh!
More specifically, it's OUTLAW and his atomic snow blower. He is able to toss frozen squirrels all the way to the Mexican border.
Serious now...
There has been speculation for years that North Korea could be the King of the North. The problem with North Korea is once Kim Jong Ill is dead, that nation could crumble. Another speculation is China because of their population, cheap labor economy and nukes. Again, not a perfect fit, because if China's largest buyer of goods folds, (USA) they would face economic collapse too. Then the speculation turns to India, another giant population with cheap labor and nukes. India so far hasn't proved to be a big player in world events, and currently seems more interested in the Kashmir territory it disputes with Pakistan. There is also speculation about Iran or one of the other Middle East nations being the King of the North. As unstable as their governments are, at best, they could only cause more terrorism, not dominate the USA who is supposed to be the King of the South.
As stated before, Watchtower has not said who the new King of the North is. They won't do so until there is an obvious candidate. Frankly, Watchtower has stayed far away from publishing anything that would declare a King of the North for fear of being wrong. So much for having God's backing!