The Council of Nicaea set the rules for determining the date of Easter...which is why Pope Gregory's calendar reform in 1582 was designed to return the date of the vernal equinox to where it had been in A.D. 325 rather than to where it was in 46 B.C. when Julius Caesar reformed the Roman calendar.
That the Anglo-Saxons, when they became Christians, took over the name of a pagan spring festival and applied it to a Christian feast is unimportant. Likewise, the English word "Lent" originally just meant "spring"--other languages have a term for Lent based on the number 40 for the length of Lent.
Dutch lente means "spring." The Dutch word for Lent is vasten, from the word meaning "to fast."
The connection between Lent and spring is that it is the time when the days are growing longer--etymologically it is connected to "long" and "lengthen." Doesn't work in the southern hemisphere.
I was referring to the ‘holiday’ Easter. Christians have celebrated thr Resurrection since it happened. However, my point was that local customs became attached to it as Christianity spread. Constantine made an official holiday to end the controversy then, as he established the modern day canon with the Council of Nicea. He established the early rules, including stopping the slaughter of Christians to end the controversies. However, the discussion here was the question of the Pagan origins of the Easter Holiday, not the resurrection and its relationship to Passover.