Hello Joshua,
I understand that you are trying to use the MCAN receive and transmit blocks for TMS320F280039C.
This feature is not supported right now.
You can use the MCAN feature in 2838x M4core which is CAN FD.
Please refer to the following link to access the 2838x M4core documentation: Model Configuration Parameters for Texas Instruments F2838x (ARM Cortex-M4) - MATLAB & Simulink - MathWorks India
Hope this resolves your query.