Kommentar zu Bereschit 46:10

בן הכנענית THE SON OF THE CANAANITISH WOMAN — means the son of Dinah, who had been associated with a Canaanite (Shechem). When they (her brothers) had killed Shechem, Dinah refused to leave the city until Simeon swore to her that he would marry her and regard the child she was about to bear as his own (cf. Genesis Rabbah 80:11).

ושאול בם הכנענית, it appears that all of Yaakov’s sons abided by his aversion to intermarry with Canaanites. Even Shimon also honoured this tradition. However, after he had married a woman who was not a Canaanite and had had children by her, he married an additional wife who was a Canaanite. Shaul was a son of that second wife of his. Seeing that this had been a breach of the tradition, the Torah alludes to it in considering this son as the “son of the Canaanite woman.” Our sages on 34,26 took the view that Shimon had taken pity on his sister Dinah who had been raped by a Canaanite, and married her and the son from the rape was the one named Shaul. (based on Bereshit Rabbah 80,11)

ושאול בן הכנעני, “as well as Sha-ul, son of the Canaanite.” Ibn Ezra explains this puzzling statement by saying that this grandson of Yaakov was the only one born by a Canaanite mother, as none of his other sons married girls of Canaanite parentage. Rashi explains the phenomenon as an allusion to this Sha-ul being a son of Dinah who had been raped by the Canaanite Shechem. If so, we are confronted with another difficulty, i.e. how could Shimon marry a sister by his own mother? According to a Midrash [I have not found such a version. Ed.] the problem is resolved as it is presumed that Dinah’s fetus grew predominantly in Rachel’s womb. [The Torah reports Leah only as having “given birth” to Dinah, not as having been pregnant with her. (Genesis 30,21)]