The "technically senior claim" belongs to Spanish Habsburgs TTL. It's likely that by 1675 Queen-Mother Mariana will strike an agreement with her brother the Holy Roman Emperor to send Maximilain to Spain to be raised there as a heir presumptive, if the health of Carlos II is unstable as OTL (which it likely will be), and Archduchess Maria will be betrothed to Carlos II since birth, I think.
As for Margaret Theresa in this situation, she'll be much better off being married to a brother of the King, who is just her first cousin and not her uncle, maybe she'll live longer.
I think that Louis XIV marries Margarita Violante of Savoy in 1658, since her mother's ambitions will be increased in TTL, when there is no competition from Spain and the English competitor is not of marriageable age yet (and her brother is not restored yet). The rest depends on whether Margarita is as unlucky in child producing.
Given that Margarita Violante's mother is really ambitious about the match, the dowry may include ceding part of County of Nice to France, which is likely to make it more attractive.