Ooofff, don't even bring up Poland, that's not a scenario that you're going to like. Their kings were constantly appointed by their neighbours and the like, with Wettins very much being examples of that, with their succession actually sparking a continent-wide war, where a Polish candidate actually lost and ended up getting a French duchy instead.

That whole electoral system doomed PLC to certain death, since every candidate had to promise the unwashed gentry more and more privileges, which were then used by the neighbouring powers as pretexts to interfere in Kingdom/Grand Duchy's internal affairs.

Just no. Horrible example.

Spanish throne is currently held by "House of Borbón-Anjou" - a less fancy Spanish way of saying Bourbons, descended from Philippe, Duc d'Anjou, grandson of Louis XIV. They were put on the throne basically entirely by the force of French arms, who have held of most of Europe trying to prevent it for 13 years. Almost Russian 1812/1945 level of awesomeness.