What is the role of a Cantor?
When and why did the Cantor come into place?
I believe it is realted to the fact that years back many people didnt know how to read or didnt own a siddur so the chazzan was the one who read on behalf of the kehal
The Leviim had the role of singing in the Beit Hamikdash.
Today being a cantor in a synagogue is not directly related to the job of singing by the Leviim but simply a function of a person whose profession is to lead davening.