LPC2129 CAN bus interface to OBD-II
Yes, you still need to use a CAN Transceiver (Converting Bus voltages to logic for your processor). But you can better use the NXP TJA1051T/3 as you have a seperate Vio so you can directly interface with your 3.3V CAN controller in your LPC. So you don't have to convert the 3.3V of your LPC to 5vV for the MCP2551.

The ODB2 connecter in your car is in an correctly terminated CAN bus so you should not put extra termination in your device as it can create bus errors (low or high) and eventually a bus off!

Also CAN is differential 2.5 volt dominant bit 3.5V and recessive bit 1.5V on CAN high (CAN low is the opposite).