Sforno on Genesis 28:6/ספורנו על בראשית כ״ח:ו׳

1וירא עשו כי ברך יצחק, we see from here that in spite of Esau’s noting that his father had sent Yaakov all the way to Charan to prevent his marrying one of the Canaanite girls, as this was not in keeping with his blessing, he did not pay much attention to this, except that when he saw to what extent his father was unhappy about this כי רעות בנות כנען בעיני יצחק אביו, he thought that it was due to his wives opposing his parents’ lifestyles, etc., as documented I 26,35. In order to appease his parents he then went to Ishmael to marry Machalat. One of the reasons the Torah reports these details is to show that had Yitzchok objected to Esau’s marrying Canaanite girls in the first place his objection would have been effective. If Rivkah’s intervention was effective now when she remonstrated with her husband there is no reason to believe that it would not have been effective when Esau was about to get married.