Pali Canon and Agama
A more useful way of looking at it is to see both the Nikayas and Agamas as Early Buddhist text rendered in different languages (Pali for Nikayas, Sanskrit for Agamas). If you've read Ven. Analayo's work on comparative studies between the two systems, you'll see they are very very similar. Now, Theravada pretty much focuses on the Nikayas as their go-to sutta sources, while Mahayana, due to its vast number of sub-schools or sub-systems, has various focuses depending on the particular school. Some pay more attention to the Agamas, while others more on the later additions (Amitabha collections, Avatamsaka, Lankavatara, Prajnaparamita, etc...).