Holy Wars only apply to infidels (Muslims, Hindi, etc.) not heretics (Catholics, Protestants, Reformed). For everyone else, if all you want is CBs, Bill of Rights gives you a liberation CB. If you want CBs to get land, go for Imperialism as soon as you can; that means going with Absolute Monarchy, Republican Dictatorship, Enlightened Despotism, Revolutionary Empire, or Revolutionary Republic.
Ah okay, but I thought Unam sanctum allows you to get cbs against heretics? Guess it only works for catholics vs orthodox and not vice versa? It seems like a really long time before you get the tech to become one of those government types. I can't imagine how people even do world conquests. :\