One time, as France, I got a PU with Castille less than 5 years into the game.
Sadly, I was fairly new at the time, so my attempt to turn this ludicrously good luck into a WC or Big Blue Blob failed spectacularly (and the Coalition war didn't last long enough for We Bled For This either...)
Most recent game, I got Hungary as a PU while Spain, specifically a Hungary that hasn't lost a single parcel of land to the Ottomans and had even picked up a few proviences from Poland. Better still, it caused a Succession War with my Rival France, one which not a single ally of his joined, and not a single one of mine (including HRE Austira) chickened out on, leading to a defeat for them that they still haven't recovered from.