Dedonus said
To be honest, I have no idea who he should pick. Of the nations on the list, Belgium has been virtually wiped out, Hanover and Bavaria will be Prussia's b**** after this war (assuming that Prussia is trying to unify Germany). Also, after this war, I assume Italy is going to invade Rome because the ToC will no longer be in effect. So that either leaves you with Switzerland or some minor country that will still leave you weak.
Portugal's available. He could also play Canada during unification, or one of the larger Latin American countries.