Avraham was extremely careful that Yitzchak not marry a Canaanite and as we know, he married Rivkah bas Besuel ben Nachor. Yitzchak was very careful that Ya'akov not marry a Canaanite and as we know he married Leah and Rachel bnos Lavan ben Besuel ben Nachor. The pasuk in VaYeishev specifically says that Yehudah married the daughter of Shua the Canaanite. VaYigash says that Shimon's youngest son Shaul was a son of a Canaanitess.
Sefer HaYashar to Parshas VaYeishev (Chapter 45) says as follows:
"Then Re'uven ben Ya'akov went towards Timnas and took Elioram bas Evi the Canaanite for a wife for himself and he came to her. She conceived and Elioram wife of Re'uven bore him Chanoch and Pallu and Chetzron and Karmi four sons. And Shimon his brother had taken Dinah his sister for a wife and she bore him Yemuel and Yamin and Ohad and Tzochar five sons. And after that, Shimon had come to Bonah the Canaanite that is Bonah who Shimon had captured from the city of Shechem. Bonah was before Dinah and she attended to her and Shimon came to her and she bore him Shaul. And Yehudah had gone at that time to Adulam and he turned to an Adullamite man and his name was Chirah. Then Yehudah saw there a daughter of a Canaanite man and her name was Eilis bas Shua and he took her and he came to her. Then Eilis bore to Yehudah Er and Onan and Shelah three sons."
The rest of the brothers do not marry Cana'anites, Levi and Yissachar marry two granddaughters of Yoktan ben Ever. Dan marries a Moabite. Gad and Naphtali marry two great-granddaughters of Nachor. Asher marries a Yishmaelite and then a granddaughter of Yoktan. Zevulun marries a Midianite (discussed here The wife of Zevulun (Sefer HaYashar)). Binyamin marries an Aram-Zovah-ite and a daughter of Zimran ben Avraham. Yehudah then Tamar bas Eilam ben Shem and Yoseph marries Osenas.
Why was Ya'akov not so careful that his sons not marry Canaanites?
In addition, I heard that Osenas was actually the daughter that Dinah had with Shechem, which would make Osenas a Canaanite as well.