My knowledge of CANopen is very limited and I am a noob when it comes to CAN. Based Wikipedia and other articles I have read, In terms of the OSI model, CANopen is a communication protocol and device profile specification for embedded systems. CANopen implements the layers above and including the network layer.
CiA (CAN in Automation) is the organization driving canopen.
Each manufacturer can define device IDs in the messages that are communicated using CANopen ( which I guess is the application layer).
A complete overview of CAN network layers is explained here: