Looking at the current problems of forming a new government in Belgium, I sometimes think it would have been better if Wallonia ended up French and Flanders Dutch (during the 19th century at least, the situation is completely different now). So inspired by the threat about a Prussian Belgium ask, how would France at the congress of Vienna (with possibly a POD slightly before it) manage to keep Wallonia. Not the Flemish harbors or Antwerp. Britain would not accept them in french hands. Also, i don't care if the borders are exactly the borders of current day Wallonia. So Brussels can become French or not, or Liege can become Prussian/Dutch/not-French; maybe (probably) no Luxemburg split, with Luxemburg ending up in either French or German/Prussian hands; etc. So any ideas?