I must be wrong, i will say "Spanish Low Countries".
So, you have in mind other possible brides for Louis? And other possible husbands for his sister?
Maybe from Louis' bride we could have Claudia de' Medici, the sister of Cosimo II, or Nicole of Lorraine.
For his sister, maybe she would be the one who would marry Victor Amadeus of Savoy. For his sister, well, there is Charles I of England.