Genesis 10:15

And Kenaan begat Zidon his firstborn, and Heth,

AND CANAAN BEGOT ZIDON HIS FIRST-BORN. These were the ten nations, sons of Canaan, whose lands were given to our father Abraham since all seed of Canaan were sold into servitude forever. These were the ones that were given to Abraham. Their names, however, changed for the most part in the days of Abraham; here they were inscribed according to the names their father called them on the days of their birth, but after they parted according to their lands and their nations, they were called by other names. Perhaps they were called by the names of the land in which they settled, as we have explained. Likewise, Se’ir the Horite was so called because the name of the city was Se’ira. And there are many similar names. It may be that the Arkite and the Sinite did beget families but were cut off from them, and their children were, for example, the Kenite, and the Kenizzite. These became the heads of families, the entire nation being called by their name as was customary among the tribes of Israel. Now in His gift [of the land of Abraham, G-d] called the ten nations by the names by which they were known in the time of Abraham., Verses 19-21.
Proof of this, [namely, that some of the names of the sons of Canaan changed in the time of Abraham], is that the Hivite mentioned here is not mentioned in the gift to Abraham,, Verses 19-21. and yet he was among them, as it is said, And He shall cast out many nations before thee, the Hittite, and the Girgashite, and the Amorite, and the Canaanite, and the Perizzite, and the Hivite, and the Jebusite, seven nations. So also in every place [Scripture counts the Hivite among the nations that inhabited the land of Canaan]. Now the Canaanite is counted in the gift to Abraham among his [Canaan’s] children,… . Further, 15:21. but only ten are counted [there, Verses 19-21. — while eleven children of Canaan are mentioned here] — because one of his sons did not prevail like his other brothers, and so he was called together with his brother [the Hivite] by the name of his father, [thus bringing to a total of ten the number of nations whose lands were given to Abraham]. It is possible also that it was Zidon, Canaan’s first-born who was called the Canaanite together with his brother, [the eleventh son of Canaan], who did not become a nation, [thus making ten the total number of lands given to Abraham].
Do not find it difficult that the land of the Philistines was also given to Abraham — as it is …

וכנען ילד, Put (Cham’s third son) is not mentioned as having had any offspring. Our sages in Bereshit Rabbah 37,2 say that the offspring of Put was “swallowed,” (remained unidentified) until the time of the prophet Ezekiel who made mention of it in Ezekiel 30,5 where we read כוש ופוט ולוד (compare also Ezekiel 27,10) Rabbi Yoseph Kara asked Rabbi Shemuel, seeing that the family of Put was not “swallowed” (i.e. that he was not sterile) why did the Torah not mention the fact that Put did beget offspring? The answer given to Rabbi Kara was that the Torah here wanted to list 70 “sons,” i.e. descendants of Noach. We learn from the number 70 that the nations that resulted from the confusion of the languages mentioned in the next paragraph (10,32) amounted to 70. Put, including all his sons are only considered as one of these 70 nations. If the Torah had written: “Put begat so and so,” how could the Torah have written afterwards in 10,32 ומאלה נפרדו הגוים בארץ וגו', “and from these the nations on earth emerged separately, etc.?” The impression that would have been created then would have been that all these nations are offspring of the sons of Noach and not of Noach himself, as the total then would have amounted to 71 and we would have had to deduct Noach in order to arrive at the correct count. In other words, Put’s offspring’s names not being listed means that it was lumped together with the father as founder of one of the nations.

וכנען ילד, I have found one commentator who writes that Canaan had 11 sons so that his nation, including the founding father Canaan, comprised 12 tribes This is supposedly what is meant in Deuteronomy 32,8 יצב גבולות עמים למספר בני ישראל, “He sets the borders of the people in a manner corresponding to the number (of tribes) of the Children of Israel.” וכנען, Put’s offspring is not mentioned as there is no need to report on this.

את צדון בכורו, I have not been able to find a good reason for the Torah describing צדון as a firstborn, seeing that no other firstborn son of these people is described as such. Normally, the first named son is presumed to be the firstborn, so that there is no need for adding that attribute, unless we are to assume that the Torah, in naming someone as the first in a list of sons, does so because he possessed superior qualities to those of his brothers. One such example would be the mention of Shem ahead of his brothers, although he was not the oldest (5,32), according to those commentators who believe that Yaphet was Noach’s oldest son. It is possible that Tzidon did possess superior qualities when compared to his brothers, so that by describing him as the firstborn the Torah wanted to draw attention to both of these distinctions. We find something parallel in Genesis 25,13 where Nevayot is described as the firstborn son of Ishmael. We have reason to believe that he possessed outstanding qualities because his sister Machalat is not described only as the daughter of her father Ishmael, and her grandfather Avraham, but also as the sister of Nevayot, her brother. (Genesis 28,9)