Regarding France, Paris isn't necessarily a given - sure, it was an important dynastic centre under the Merovingians and the high Carolingians, but so was Metz, and that ended up as a border city. There are several possible ideas about other French capitals:
1) Laon has already been mentioned, and deserves a thought. The problem with Laon as a capital is the same as the OTL problem with Laon as a university town - sure, it's very defensible, but at some point you run into problems with the water supply... Even if an ATL Carolingian dynasty stays there for a few centuries, I imagine they'd change it to somewhere easier to supply - Rheims, perhaps, or Compiegne.
2) Somewhere like Sens or Dijon. If Ralph of Burgundy has some heirs, then you could get a dynasty of Bosonid kings whose power-base is in Burgundy rather than the north, and in that case the *French capital would presumably end up there. Given it's a wealthy, well-connected region which is already the home of Cluniac monasticism by Ralph's time even if it doesn't end up being home of an *Cistercian movement, this might well stick.
3) Even under the Capetians, Orleans is as viable as Paris - if the Normans can at any point in the tenth or eleventh centuries grab the Vexin earlier or make their hold on it stick harder, then Orleans has the distinct advantage of not being a day's march away from a well-organised and potential hostile rival potentate...
Either these, or Tours - its location is just as good as that of Paris or Orléans, and it actually served as a royal residence for a century after the Hundred Years war (so if you keep the Valois dynasty alive and in power, it becomes a possibility).