A Canon is a priest of the Cathedral Chapter appointed by the bishop to carry out various ecclesiastical functions in the diocese as directed by the bishop. There’s a whole chapter in Canon Law about the Cathedral Chapter and Canons - HERE. Some of the points it makes:
Can. 503 A chapter of canons, whether cathedral or collegial, is a college of priests which performs more solemn liturgical functions in a cathedral or collegial church. In addition, it is for the cathedral chapter to fulfill the functions which the law or the diocesan bishop entrusts to it.
Can. 509 §1. After having heard the chapter, it is for the diocesan bishop, but not a diocesan administrator, to confer each and every canonry, both in a cathedral church and in a collegial church; every contrary privilege is revoked.
It is for the same bishop to confirm the person elected by the chapter to preside offer it.
§2. A diocesan bishop is to confer canonries only upon priests outstanding in doctrine and integrity of life, who have laudably exercised the ministry.
As for a Canon in a religious order - this is not the same as a Canon of a Cathedral Chapter. “Canons Regular” refers to the function of members of a religious order. Thomas Aquinas says: “The Order of Canons Regular is necessarily constituted by religious clerics, because they are essentially destined to those works which relate to the Divine mysteries, whereas it is not so with the monastic Orders”. As the Catholic Encyclopaedia says, the clerical state is essential to the Order of Canons Regular, whereas it is only accidental to the Monastic Order. It distinguishes him from a monk who may or may not have the clerical state.