The Bishop's Wife
One of my favorite Christmas films is "The Bishop's Wife" and yet I never encountered it as a child. [The title may have scared me off.]
I understand that there was some initial confusion as to whether Cary Grant and David Niven should switch parts. Fortunately, sanity prevailed. Loretta Young was also excellent - here are the three of them in a non-trailer trailer - but the big scene stealer was Monty Woolley.