Rashi on Bereishis 24:39 says that
Abraham said to [Eliezer] “My son is blessed, and you are cursed [Eliezer was a descendant of Canaan who had been cursed by Noah], and an accursed one cannot unite with a blessed one.”
And Rashi on Bereishis 24:8 says that if Eliezer does not find a suitable match from Avraham's father's house then
take him a wife from the daughters of Aner, Eshkol, and Mamre
So since Aner, Eshkol and Mamre are also descendents from Canaan who was cursed, why did Avraham prefer their daughter's over Eliezer's?