In Mark 3:18 and Matthew 10:4, the the King James Bible has Simon as a Canaanite.  However, in Luke 6:15 and Acts 1:13, the KJV has Simon as a Zealot.  These are not really compatible to be mutually co-existent, since Jesus would not have appointed a Gentile to be one of the Twelve, or one of the names on the twelve foundations of the New Jerusalem in Revelation 21:14.  In teh Matthew passage, in the very next verse, Matt. 10:5, Jesus tells the twelve not to go down any Gentile road, but to go “only to the lost sheep of Israel.”  Jesus surely would not tell a Gentile that.  Moreover, since the KJV admits that Simon was a zealot, this is also unlikely, that a Gentile would be a Zealot, one of the factions of Judaism.  The earliest manuscripts of Matthew and Mark say Simon was a καναναῖος, which word was derived from the Aramaic word for Zealot.  And the Textus Receptus and the Byzantine text have Simon a Κανανίτης.  Strong’s Concordance for this word, G2581, says this word also is derived from קנּא kan-naw’, “Jealous.” Canaan in Greek consistently starts with the letter Χ :

Canaan (ie., Genesis 13:12) Χανααν; Canaanite: Χαναναίων (Genesis 10:18) Χαναναίους (Genesis 15:21)  And in the NT, for the Canaanite woman, Matt 15:22, Χαναναία

BDAG Lexicon: “Κανανίτης, ου, ὁ man from Cana, Cananite. Acc. to Strabo 14, 5, 14 one of the two Stoics named Athenodorus received this name to distinguish him fr. the other Ath.; ἀπὸ κώμης τινός (Cana near Tarsus) was added. Numerous mss. replace the apparently unintelligible Καναναῖος with this term.” Under Κανά it says the home of, “according to many, also of Simon, Mt 10:4 (s. Καναναῖος). – Heinz Noetzel, Christus und Dionysus ’60. – EDNT.BBHW II 926. M-M.”

The bottom line is that both variants apparently mean the same thing: someone from Cana.  The KJV saying Canaanite is simply rendered incorrectly in English.

I have updated my footnotes on the pertinent passages in Matthew and Mark.  They are linked for downloading.