Can a raccoon attack an opossum?

No. True possums live in Australia and other regions of Oceania, where there are no raccoons. The term is sometimes used as a synonym for "opossum", which is a different animal.

A totally different question is, "can a raccoon attack an opossum?" The answer is, yes, if it feels threatened.

There are true opposums in both North and South America. They are not only found in Australia.