Assuming that both England and Scotland will stay catholic, and enter XVII century as major catholic powers (I think the best POD is to have Henry XVIII beign succeded by his son by Catherine of Aragon - that should also change James V's fate and), how different the balance of power in Europe during late XVI/early XVII century would have been? Are potential catholic sons and daughter english kings good enough for Habsburgs? How different Thirty Years' War is in this timeline? Would England support Spain against France, France against Spain, or try something different? And how potential Anglo-Scottish union would have beign without any religious problems?