I'm really not sure who the audience for this is. It's based on a film from the 50's, which had Doris Day in the lead. I would have guessed they'd market this to maybe an older audience, or families, who have a bit more fondness for the film... but that demographic likely aren't going to be wowed by Tom from McFly's sister. Similarly, I don't think Carrie's target audience are going to be clamouring to see this kind of musical unless it's specifically to see her (are we going to have tantrums when someone complains that the alternate is on? "You paid for Calamity Jane and you got Calamity Jane!").
The last time this toured with Jodie Prenger, it apparently sold well but didn't get fantastic reviews...and that's with Jodie Prenger, who, at least at the time, was a lot more well known for winning I'd Do Anything, and is a lot better on a technical level than Carrie.
A production like this can work (the production of White Christmas with George Blagden I saw in Sheffield last December is coming to mind) but it hinges on the charisma of its leads... and Carrie ain't got it.