Sutton has starred on one TV show, which is great, but I still don't assume she's the kind of household name that Jackman is. Jackman is the draw, especially for ticket buyers that aren't die-hard theatre goers. (Again, no aspersions on Sutton, who will appeal much more to those who know her from previous Broadway roles.)
And yes, I'm sure that film and TV will start up first.
But I still don't think that means that The Music Man can't premiere without either or both of them. Having Jackman headlining the show is a big thing for ticket sales, but I'm sure they could find another name if they had to.
But god willing, the show will go on with the currently planned cast in place.