with a Pod after the Islamic conquest of Iberia and before the Habsburgs have Iberia united under 1 ruler, culture, language and religion.
Not that hard, but it would require a more unified southern Gaul, for exemple with a surviving carolingian Kingdom of Aquitaine that would still keep Pyrenean counties.
It would certainly prevent the kingship and loyalties dispersions that existed IOTL between, say, Navarra, Aragon, Sobrarbe, Catalan counties, while the Hispano-Romance entities were more usually tied together even when their kingship were distinguished (it's why Castille and Leon so regularly united again after a split).
Eventually, at the exception of parts of the peninsula under Aquitain or post-Aquitain states (and then possibly to be taken back, even with a really more important distinction between these than with Catalans and Castillans).
I'm inclined to disagree. Regarding France, after the Frankish conquest, in a very simplistic assessment, we had a twofold cultural divide: the northern Frankish (langue d'oil speaking) people and the southern post Gallo-Roman remnants, which eventually evolved into the vague collection of Occitan identities (langue d'oc).
These are mostly linguistical divides, not cultural ones. Culturally, Oc and Oil were really, really close from each others, sharing many features trough mutual influences since the XIth century, while "identitarian" cultures were still mostly regional (and actually got more diverse with the XIVth century).
South of the Pyrenees, there were Basques (fairly alien to any of the European peoples)
See below.
, the "post-Visigothic" regional identities (which formed the basis of Castillian, Leonese and Galician),
These can't be seriously adressed as post-Visigothic. They were the continuity of Hispano-Romance identity (that get called Goth by the VIIth century eventually), with even less germanic influence that they appeared in the northern highlands with a close cultural and political proximity with Basques.
On which should be noted weren't seen as foreigners by the Northern Christian principalities (while they were such for Goths), but as one of them (Kingdom of Navarre/Pampelune), interacting on same level (as they did in France).
Linguistics didn't have really a huge identitarian weight by the classical middle ages.
but the religious separation one was something no realm in Western Europe had to deal with.
It never really harmed what existed in, say, Sicily. The problem wasn't the cultural differences (again, a LOT of mutual influence/interference, mostly trough Neo-Mozarabs and Christian mercenaries), not that they didn't played a huge role, but that political ones eventually prevailed
politically : the legitimacy of the caliphe/emir/sultan was to break Christians, while the royal legitimacy was about taking back Hispania.
1) The Muslims conquer the entire peninsula. Christians become a tolerated minority, but until the 1500s they are actually absorbed into the Muslim population, ruled by the Cordoba Caliphate.
Arabo-Berbers did that IOTL. In spite of more or less successful revolts, it's likely that they still get the northern highlands under a more or less important watch until the Great Berber Revolt