Hello Lenni. Thank you very much for your encouraging words concerning this initiative to complete the newly created avenue to make Arduino Due to get seriously involved with the CAN standard.
In reference to your first suggestion, as too many of us know, CANopen is a higher level CAN bus protocol. Even thou both use the CAN 2.0B standard for the physical and data link layer, that's it. They differ from the other five layers in the OSI model. I am completely agree with you about implementing CANopen but we are in the incipient phase in building this interface, so, one step at a time. I believe the help from people like you will be needed very soon. I have planned to take advantage of what is inside the ATSAM3X8E, two can controllers that provide all the features required to implement the serial communication protocol CAN as referred by ISO/11898A that includes 1.0 Part A and 2.0 Part B.
In reference to your second suggestion, yes, it will be necessary a couple of transceiver like SN65HVD234 to provide the required transmission capabilities between the differential CAN bus and the CAN controller. I am taking notes of your comments and other comments from this community to keep in mind. Thank you again.