This song.
I can’t find it, and soundhound is not getting anything. I think it is ‘believe’ by Josh Groban but his version has words. I’m looking for that instrumental version’s title and performer.
Alan Silvestri had scored the film. The producers, deciding that they needed a song to go over the closing credits, commissioned Glen Ballard to write some lyrics to go along with the motif from the opening sequence.
As near as I can determine, the performance is by a pick-up orchestra comprising a bunch of studio musicians.
ETA: As far as a title is concerned, I suspect that it would be on the soundtrack album as track #14: Suite From The Polar Express, by Alan Silvestri