Recently I've watched "What if Poland was a Superpower" by Whatifalthist and one of the postulated effects of the Polish-Lithuanian Commonwealth remaining the powerhouse of Eastern Europe was that Prussia would never have the chance to become its own kingdom.
Assuming that had actually happened, what other OTL state, Austria aside, would have had the best odds of managing to fit in Prussia's shoes?
Assuming that had actually happened, what other OTL state, Austria aside, would have had the best odds of managing to fit in Prussia's shoes?