Agreed about the EU. And I don't think Russia will be a challenge; but if it's going to be, it'll take it at least a couple of decades (my personal hunch is that Russia's demographics and various border conflicts will make it weak and underpopulated, a real temptation for China to move in there ... I'd rather not see that happen).
Yes, CHINA. That is one country I will never trust.
Radical islam is another threat to Russian borders as well. But that is obvious.