I think a weak and loose Federation that is really not much more than a custom's union under a common King is the most we can do.
1800 - France doesn't occupy Spain, holding off the worst of the Revolutionary outbreaks.
1830 - Spain is falling apart and can't even pretend to hold New Spain by force. Agrees to greater and greater degrees of autonomy under the crown. Effectively, the assorted states fo New Spain become self-governing commonwealths akin to Canada and Australia.
1800 - France doesn't occupy Spain, holding off the worst of the Revolutionary outbreaks.
1830 - Spain is falling apart and can't even pretend to hold New Spain by force. Agrees to greater and greater degrees of autonomy under the crown. Effectively, the assorted states fo New Spain become self-governing commonwealths akin to Canada and Australia.