@Yogurt_Man thank for your your reply. I saw the CAN2DYNAMIXEL example and it inspired me to try a different approach on the Rotortug (only on my testbed) with two Arduino MKR boards + CAN-Shields + Dynamixel Shield (I red-boxed both the MKR’s and the CAN connection in the picture):
What I have in mind for the TurtleBot3 is a bit different, since the OpenCR board there should finally run the Arduino port of micro-ROS and connect to other MCU’s via CAN. But before diving into micro-ROS I would like to kown the board hardware better… 
Using CAN to connect different MCU’s, SOC’s (like Raspi’s) and even PC’s could be a real game changer for my project. The MCU (STM32F103CB) of the OpenCM 9.04 does have a CAN controller, but that’s not mentioned in the eManual, too (maybe it’s not even HAL-connected to a board pin).