Some assume that Tamar might be a Canaanite because she lived in Canaan.  She was the mother of Perez & Zarah by Judah, her father-in-law.  However, it was Judah who married a Canaanite woman named Shuah (Gen. 38:2 & 12) who bore him 3 sons, Er, Onan & Shelah making his 3 sons half Canaanite.  

However, the origin of the name Tamar is Hebrew and means "date palm."  King David also had a daughter named Tamar who was the sister of Absalom (2 Samuel 13:1), and Absalom had a daughter named Tamar (2 Samuel 14:27). 

If Judah hadn't broken his promise to Tamar and she had been allowed to marry Shelah, Judah's 3rd son, and they had children, they would have been 1/4 Canaanite and 3/4 Hebrew if Tamar is Hebrew.  However, if Tamar had been a Canaanite, their children would have been 3/4 Canaanite and 1/4 Hebrew.  But if Tamar is really a Hebrew woman, then her children by Judah, a Hebrew, would be 100% Hebrew.  The Bible does not say why Judah never married Tamar.  Judah was a widower at the time, and Tamar was a widow. Gen. 38:6 tells us that "He knew her again, no more."  Was he afraid of dying like his first two sons?  In any case, his third son Shelah must have married because he had 5 sons according to 1 Chronicles 4:21-22.  He was never given to Tamar to be her 3rd husband.

It is interesting to note what Zechariah 14:21 says in regards to the Canaanite, "Yea, every pot in Jerusalem and in Judah shall be holiness unto the LORD of hosts: and all they that sacrifice shall come and take of them, and seethe therein: and in that day there shall be no more the Canaanite in the house of the LORD of hosts."

As a side note, one of Jesus' disciples was Simeon, the Canaanite according to Matthew 10:4 & Mark 3:18.