Esparza has none of the charisma and smoothness needed for the role, he's tough, harsh, and has the potential to be incredibly hammy. In a role like this, you need someone who can be hammy and make it work (the Stephen Colbert idea is brilliant, he was great in the NYPhil COMPANY), Esparza would suck the fun out of it.
Speaking of Esparza, an unconventional Harold Hill--sort of in the mold of Daniel Radcliffe--would be David Hyde Pierce.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"