“the Canaanite.” The Canaanites were descendants of Ham (Gen. 10:6), although in this context it means more than just that the descendants of Ham’s son Canaan settled there (see commentary on Gen. 12:6).
“Perizzite.” A tribe of unknown origin that by the time of Joshua lived in the hill country of Judah and Ephraim. See commentary on Joshua 9:1. The Canaanites and Perizzites were wicked people, and would have been a threat to Abraham. Also, this lets us know that if there were Canaanites and Perizzites in the land at the time of Abraham, when Israel crossed the Jordan River and entered the Promised Land some 400 years later they would have had time to multiply greatly, which they did.
“were living in the land at that time.” This use of “land” is more specific to the part of the land where Abram was at the time, not the whole area of the Promised Land.