In my experience with AE, the typical usage is to use the word "Passover" as both a noun and an adjective if referring to the Jewish feast. Thus, if one is referring to the meal eaten by Jews (including Jesus), the Passover meal would be the common expression.
If you are referring to the specifically Christian celebration of Christ's resurrection, then people usually use the term "Easter" as both a noun and an adjective.
The noun Pasch and adjective Paschal are possible, but represent a much more formal usage, that I would expect to find only in the context of a liturgy, such as the church services for Holy Week and Easter. Keep in mind that in the Romance languages, the usual term for Easter is derived by the Hebrew word for the Passover. Thus in formal church usage, Easter may be referred to as the Pasch and the adjective Paschal may be employed (e.g., the Pascal candle).
Among some AE-speaking Christians who are Eastern Orthodox or Eastern-Rite Catholic, there is a preference to use Pascha (another variant of Pasch) and Paschal, rather than the word "Easter."