OTL, when Elizabeth died at the beginning of the 17th century, the Stuarts went south to London and for all intents and purposes, the British Isles were under a single king. My question relates to how long could they be kept as two separate kingdoms under two separate dynasties? Are they doomed to an intermarriage policy a la Spain-Portugal? Or would they follow two largely divergent policies like Denmark and Sweden until the 19th century? As a side note, what are some of the more interesting marriages that can dynastically unite the two kingdoms? I'm ignoring the oft-toted Edward VI-Mary, Queen of Scots match (since that's sort of boring - while a union happening through Bloody Mary's half-Habsburg child and Mary, Queen of Scots' Valois kid is less so, for instance). It'd be especially funny if the crowns end up on the same head through accident and happenstance.