Germany/Japan

This is not one of the most well known couples in Hetalia, although it has potential to be canon.

The two countries, looking upon real history, have had secret relations documented back to the Tokugawa Shogunate. Their relationship was most likely strained after the events of World War II, however that doesn't mean that their relations are /still/ strained.

Actually, it's quite the opposite.

The two countries now have a wonderful relationship, sharing similar interests in things such as science and technology. There is even a street in Germany named after Hiroshima.

If you would like more info on the real relationship between the two countries, look up German Japanese Relations and you will see that their relationship is a rather strong one. Many people have even gone as far as saying that if Hetalia followed history a little better that it is quite possible that Germany and Japan would be one of the much more canon couples of the series.