What is the use of series resistor in VBAT line of CAN transceiver?
It forms a filter with the capacitor right next to it, making sure that any noise on the Vbat line does not get inside the chip and out again through the signal lines that Vbat is used for (INH and WAKE).

Since Vbat is not used (AFAIK) for power, the resistor sees low current. 

You should use an RC couple such as the cutoff frequency is well below the potentially problematic frequencies of your circuit (Power supply, microcontroller clock, CAN bus, etc.)