I can imagine how someone could guess the tags (like, probably it was between the pixiv tags) but can you really tell who is who?, I guessed Japan (because of his clothes mostly, and hair) italy and germany (behaviour)Romano (ahoge, and looks like his bro)and América (behaviour) but I couldnt tell UK o.o, I searched this image just to see the tags and find who he was xDD
I'm not sure if the picture is RussiaxJapan or AmericaxJapan. I see a person resembling America (he has that cowlick) running with Japan's dog. And judging by the hair style I'm almost sure the one with Japan is Russia.