I believe the industrial heartlands where most of the money was was in the Walloonish areas, while the capital had French forced upon it, and for the administration of their colony. I don't know if they would want to go against France for Flemish lands which would simply lower the power of the Francophonics, unless of course you tossed in the lands of Picardy nearby where they spoke Walloons... Of course their is one, major problem. Since beginning of the Napoleonic wars, Prussia would stab nearly every one of their allies in the back in order to seize their land. I do not think the Belgians, with one of the most valuable areas in Western Europe, would be very confident in the promises of Junkers. Might also be problems given the treatment of Catholic Poles and Germans in Upper Silesia and the Ruhr.