To answer your question directly, Helen, I've never eaten a PB & banana sandwich in the USA, nor do I know anybody who has.

But I don;t know everybody, and they don't always tell me how they eat their PB sandwiches.

I've always eaten the standard PB&J, or sometimes PB & honey (mmm!).

I seem to recall, however, that Elvis Presley used to eat the PB & banana version - often with bacon added!

I'll try one and get back to you.