There are two songs specifically set for Easter Sunday in CWB II. Then there are a plethora of general Easter songs that I’ll tackle a bit at a time.
344 Easter Sequence: Christians Praise the Paschal Victim
The original words are a thousand years old by Wipo of Burgundy, here translated by Peter J. Scagnelli and in copyright (WLP). The chant tune is public domain.
You can see the chant notation here, but note that the text above is a different translation.
… or in Latin:
345 O Flock of Christ
This is a very different translation of the same sequence by James Quinn and set to VULPIUS.
It is available in this collection at OCP. I can’t find a link to the text anywhere.