Given that he is used to living under a French-speaking elite with a largely Germanic-language speaking population, I would say that Luxembourg would be his best bet.  Moreover, Luxembourg is by far the richest 'territory' in Europe.   On the other hand, Germany and France are much bigger (but poorer) than Luxembourg, so that the 'economic base' for future subsidies (in absolute terms) to Mr Kempen would be much bigger in those two countries. 

Perhaps he should organise an auction, and see who will offer the best terms to the former 'East Cantons'. 

The Belgium federation must be preserved at all costs so Father Kempen will never need to make the hard choice about where he shall go to.