Why Avraham will not let Yitzchak marry a Canaani woman

We learned in class that Avraham is very adamant that Yitzchak cannot marry a Canaani woman. Avraham also tells Eliezer that he must not let Yitzchak go with him to find a wife. Why? We discussed a few possibilities. The first is that the Canaanim were not moral and ethical, and in order to continue G-d's promise and Avraham's legacy, Yitzchak must marry someone moral and ethical and not be influenced by them and any other outside influences. The Canaanim are also not one of the chosen generations. They are nidche, and Yitzchak must marry someone that is nivchar. If he marries someone that is a Canaani, he might go and stay there, and if so he can't spread ethical monotheism or inherit the land.