I had read somewhere that the Habsburgs had been excluded from consideration, but I wonder if Maximilian would have been considered had he never been Emperor of Mexico.
I'm working on a scenario where the Reform War, a civil war in Mexico that occured few times before the French expedition, has been won by Conservatives and where no monarchy is set up.
In families where ''finding a democrat is as easy as finding an atheist in heaven'', Maximilian was pretty liberal and could suit the role, and Napoleon III would support it as a mean of strengthening the French-Austrian alliance.
Is that plausible?