Point of setting the record straight:
(Ghost) Riders In The Sky shares ONLY the first two melody lines of the verse (an none of the chorus) with "When Johnny Comes Marching Home"/"Johnny, I hardly knew You."

The rest of (Ghost) Riders is quite different, not just in rhythm, tempo, etc., but in melody as well.

I'd add that while "I Can't Help Falling In Love With You" may be derivative of "Plaisir D'Amour," the tunes are hardly identical. (I'm not even sure you can use the same chord pattern for both.) Not to mention that ICHFILWY has a bridge, with its own melody, that has no relationship to Plaisir D'Amour.