But I only know how it was spelled from my FIL's photo album. If I had only heard him spoken of I wouldn't know if he was being called Louie or Louis. Anyway, if I as a USian don't know which pronunciation to default to (even for RLS I had to stop and think which one I say), it's either not universal or never was. I can certainly envision a French-Canadian kid in the US being called Louis at home and thinking of it as Louis, and an Anglicized pronunciation (but no final S) at school and everyone there thinking of it as Louie. Similar to my half-Greek friend Melanie, whose mother called her Meli, meaning honey, but who was also sometimes called Melly as a nickname.