Hey there, I was close to giving up on this but seeing that others are also struggeling I am willing to keep on trying.
Here is what i figured out: the two can pairs on the breakout board are traced as follows:
CAN1_TX --> HD Connector 49
CAN1_RX --> HD Connector 51
CAN0_TX --> HD Connector 50
CAN0_RX --> HD Connector 52
On the portenta H7 board itself only connections for CAN1 are made:
CAN_RX and CAN_TX translate to PIN D5 and D16 of the MCU:
which should be PB8 and PH13 just as @jlaustill also figured out.
However i also cannot get it to run and at this point I tried multiple transceivers as well:
SN65HVD230 like @jlaustill
TCAN1044AEV-Q1
TI ISO1050 Isolated CAN Transceiver
all without success... tderrors just keep happening the same as if no transceiver is connected.