What are the connotations of not entering into a covenant "with them and with their gods"?
Ramban #1: It is a prohibition against leaving any Cana'ani alive and any of his idols intact.
Ramban #2: It means not entering into a covenant with them to keep them alive - as long as they adhere to their gods, but not once they relinquish them.
Oznayim la'Torah: In case you say that you will make a covenenat with them
Oznayim la'Torah: Like Sh'lomoh ha'Melech said 'I will mary more wives and I will not sin!'.