How do the sons of Kena'an listed here, tally with the ten nations that HaSh-m would promise Avraham (at the Bris Bein ha'Besarim (15: 19-21))?
Ramban: The names here are those given to them at birth; most of the names were changed already in the time of Avraham (perhaps they were called after the name of their respective locations), and it is the changed names that are listed in Bereishis 15.
Peninim mi'Shulchan ha'Gra (Bereishis 15:19): The nations Arki, Chivi Arvadi, Tzemari and Chamasi mentioned here, are the Perizi, Refa'im, Keini, Kenizi and Kadmoni there. Tzidon and Sini are not mentioned there, for they were north and south of the land promised to Avraham. Edom, Amon, and Mo'av took the land of Keini, Kenizi, and Kadmoni. 1 Due to the sin of the Meraglim, Yisrael will receive them only in the future. 2
Since one of the nations mentioned in the time of Avraham (Bereishis 15:19-21) is called "Kena'ani" (after the father of that nation), there ought to be eleven nations in that list?
Ramban: One of the ten nations mentioned here, presumably Tzidon (the firstborn), was called Kena'ani after his father.
How will we account for the fact that eleven names are listed here?
Ramban: That is because one of the ten was too small to become a nation, so he combined with Tzidon to become part of the Kena'ani.
If the rightful owners of Eretz Kena'an were Yisrael (see Rashi to 9:26, Rashi to 12:6), what were the Kena'anim doing there?
Rashi (in Bereishis 12:6): When Noach distributed the world among his children, he allotted the area of Kena'an to Shem; Kena'an (temporarily) captured it from them around the time of Avraham's arrival.
Ramban #1: The land was initially given to Yisrael. 1 When HaSh-m divided up the world, in the time of the Dor ha'Palagah (the Generation of the Tower), He gave it to their Eved, Kena'an, to look after, until they would be ready to take it over.
If Avraham was promised all the ten lands of the Kena'anim exclusively, how is it that the land of the Pelishtim (who were descendents of Mitzrayim) is included (as HaSh-m will specifically tell him later (See Bereishis 26:3)?
Ramban: The land belonged to Kena'an, only the Pelishtim captured a section of it. 1
I.e. the five major cities of the Pelishtim (Ashdod, Aza, Ashkelon, Gas and Ekron). And it was only that part of the Pelishtim's land (plus Tzidon, which the Pelishtim subsequently captured) that HaSh-m promised to Avraham.
Why does the Pasuk not list the sons of Put (the third son of Cham)?
Rashbam (et. al.): Refer to 10:6:1:1.