Austria-Hungary would definately be a bad idea. I doubt either Austrians or Hungarians would be pleased to have their country be "shared" by another. Austria is already represented by Germany; England could be changed to "The United Kingdom" to represent Scotland (and the Celts, for that matter); Portugal, as powerful and important as it was, could be re-assimilated into Spain; and the Netherlands really had little impact on European civilization (not for lack of trying, but just because they were completely dominated by Spain and the like). There is a good argument, however, for the Poles and the Hungarians; the former almost became a superpower earlier on, and remained a driving force behind much of Europe's wars, treaties, and foreign policies; Hungary was a superpower for a few hundred years, after which it kept the Ottoman Empire at bay, becoming "the savior of Europe." Both countries now play major roles in modern global civilization; indeed, Poland and Hungary are the most powerful of the Eastern European nations. Most importantly perhaps, neither of them are culturally very similar to other nations, such as Spain/Portugal, Austria/Germany, etc.
Apologies for ressurecting the thread.
