Voltage drop across power supply rail
The CAN buss ICs are designed to tolerate much more than 1% vdd drops.

You need to reduce the I*R drops by 5:1 or 8:1.

Each square of PCB foil is 0.000500 (1/2,000th) ohm. You should account for that I*R voltage drop in your multi-PCB system. A trace between Input connector and Output connector, of size 2" by 0.05", has 40 squares of resistance, thus 20 milliOhms.

At 1 amp, the I*R drop is 20 milliVolts.