The person holding the Easter Candle should sing “Christ our light”. But I do not think that the priest must be the one holding the Easter candle.
I think the 2002 Roman Missal gives more flexibility than the 1975 Roman Missal had. According to the 1985 Roman Missal translation, for the Easter Vigil: “14. Then the deacon or, if there is no deacon, the priest takes the Easter candle, lifts it high, and sings alone: Christ our light.”
But the 2002 Roman Missal has: “15. … Diaconus vel, eo absente, alius minister idoneus, accipit a ministro cereum paschalem et ordinatur processio. …”. There is not yet an official translation, but what I think it says is: “15. … The deacon or, if absent, another suitable minister, receives from a minister the Easter candle and leads the procession. …”.
There does not seem to be a requirement to use a priest in the absence of the deacon, because the word “sacerdos” is not used. So I think it would be OK, in the absence of a deacon, to have a cantor carry the Easter candle.
References:
The Roman Missal, Catholic Book Publishing Co., New York, 1985, page 173.
Missale Romanum, Libreria Editrice Vaticana, 2002, ISBN: 8820972719, page 340.