My suggestions: Timberlake/Foster, or Lin-Manuel/Foster.
And thinking of two people who made Broadway debuts this year and who have ties to NBC? Zachary Levi and Zach Braff, though both probably read too earnest for Harold Hill.
Norbert Leo Butz & Sutton Foster. Boom, done.NBC's version: Zach Braff and Taylor Swift.
I would think Levi could handle it--his voice acting as the cad in Tangled was solid.
His ties to CBS might muck it up, but Johnny Lee Miller would be a good HH along side Sutton Foster's Mariam. I'd love to see Audra play Marian. Hell, let her and her hubby, Will Swenson, take the leads; that'd be fun. Or Cheyenne Jackson. I agree w/ Finn that NLB is kind of perfect for the part, but I'm guessing they'd cast him as Marcellus.
I've never seen The Music Man, but, after last night, I'm proposing Dinklage in the male lead, and, in the female lead, also Dinklage. I know that's gonna be tough in a live show, but I have faith in Dinklage.
Foster as Hill, Milioti as Marian.
Not an a-list celeb, but Kate Baldwin did a lovely Marian Paroo in the Arena Stage (DC) production a few years ago.
Kristen Bell could make a great Marian. She proved with Frozen that she can sing it.