Yes, Rick, Durbin turned down the role that went to Susanna Foster.

I've been reading Jeanine Basinger's The Star Machine, which details the way movie stars were "discovered," developed, and maintained.  It's really fascinating and Basinger's insights are too.  Just last week finished the section devoted to Durbin whom Basinger refers to as the real Greta Garbo, a star who truly walked away from Hollywood and faded into anonymity.  She's one of those stars forgotten by today's mainstream public but crazy popular in her day.  All but about one of her films made bundles of cash for Universal. 

Oddly, I've never seen a Durbin film.  I don't recall them playing here locally.  The closest I've gotten is to Durbin's "replacement" (if needed), Gloria Jean in Never Give a Sucker an Even Break.  Even more odd, after having just read the Basinger account, a Deanna Durbin DVD set just came into my store a few days ago and is sitting in my holds waiting for me to check it out.

By the way, Durbin's Deanna moniker came from her mispronunciation of the name she really liked, Diana.