Differential audio (aka balanced audio) doesn't hum in presence of ground loops, and Just Works as long as ground differences are within the common mode range of audio opamps (say, around +/-12V for example).
CAN is differential like differential audio is, so the same applies.
If you have high-current devices that have separate power and communication connectors, isolation of the comms may be a good idea because if non-isolated, disconnecting the power wire but leaving the communication connector provides a power path through the communication connector which may not be rated for such high current. At least use fuses to prevent damage.