Canterbury is definitely Catholic. They are a little more progressive (as most boarding schools are), but they do focus on their Catholic roots. With that said, if you are not Catholic, you don’t feel out of place at all. Their campus is beautiful and they have a brand new student center - windows across the back side of the building so you can see the amazing landscape at all hours.
Trinity Pawling is an Episcopal School, I believe. It is definitely not Catholic. I don’t recall there being any mandatory chapel requirements when we were touring. Another beautiful school, though.