Or HaChaim on Genesis 12:6/אור החיים על בראשית י״ב:ו׳

1 ויעבר אברם בארץ. Abram traversed the land. The Torah informs us that Abraham kept moving from one location to another without any of the local inhabitants challenging him. This in spite of the fact that the Canaanites ruled in the land at the time.

2The verse also hints that Abraham behaved like an itinerant traveller, not pretending to be a man of stature. This characteristic of Abraham came to the fore later when others refer to him as אברם העברי, Abram the transient. The reason that the Torah mentions the presence of the Caaanite in the land only in this verse, and not in verse 5 where we would have expected it, is to indicate exactly when the land of Israel passed into the hands of the Canaanites (having previously belonged to the descendants of Shem). The fact that the expression ארצה כנען is used already in verse 5 means only that the Torah refers to the name the country would be known by subsequently.

3Possibly the word כנען which has a numerical value of 190 is an allusion to Abraham and Sarah being 100 and 90 years old respectively when Isaac was born. The idea that this land would eventually be transferred to the Israelites therefore is already part of its very name. The latter became potential owners once Isaac was born.

4Another lesson from the mention of the Canaanite "then being in the land," is that the Torah reminds us that Canaan was a slave, having been cursed by Noach who decreed that he should be עבד עבדים, "a slave to slaves (Genesis 9,25)." Slaves do not possess property rights. The Canaanite taking over the land from the Semites eventually opened the way for the Israelites to dispossess, them. The Semites, who had come by the land legally, would have presented G'd with a legal problem He had to solve before He could have disposessed them. Our sages have said that inasmuch as Abraham was a Semite, expelling the Canaanites and having the Israelites take over the land was only a return of the land to its rightful owners. Accordingly, the Torah phrases its description of the Canaanite presence in the land in such a way that the world understands that such a presence was never legal (compare Rashi and Nedarim 32).

5Another reason the Torah mentions the presence of the Canaanites as conquerors in the land is to contrast this with G'd's promise to give the land to Abraham's descendants. Had the Torah not informed us of the fact that the descendants of Shem already lost most or all of the land to the Canaanites, we would not have considered G'd's promise as something special, seeing that Abraham was a descendant of Shem and as such already had a legal claim on that country.