This one should be easier to guess than the Bella Spruce post. Both Polly Byrnes and Robert Landis actually play in the movie you should guess. Polly sings two songs in the movie Smoke Dreams and Blow That Horn.
And if you don’t know it already, I’m sure you know it after reading the following quote:

“You see, when it comes to words like that, an illiterate person…”
“Whaddaya mean “illiterate”? My father and mother were married right here in the city hall!”

This is from a movie of the late 1930s. But beware neither Bella Spruce nor Letty Finhadden actually appear in the movie. The female protagonist only claims these names to confuse her husband. Here’s a quote from the movie to make it easier for you to guess which movie I’m talking about:

“Why mommie, you know better than to come to a place like this your first day out of bed. What if the health officers find you? They’ll put you right back in quarantine.”
“I won’t stay in quarantine. I don’t care who catches it!”