Hi Jony,
The simplest way to build a box that can transmit/receive data between CAN bus and ethernet connector is making use of CAN Transceiver chip that is common to nxp-freescale products you can have this basic schematic -> "CAN Transceiver with MCU()":http://schematics.com/project/high-speed-can-transceiver-18566/
You can also have NXP chip with Ethernet and CAN options, same to this one
-> "NXP ColdFire('')":https://www.nxp.com/products/microcontrollers-and-processors/additional-processors-and-mcus/coldfire-plus-coldfire-m/coldfire-processors/coldfire-v4-mpus/coldfire-v4e-microcontroller-with-ethernet-can-and-encryption:MCF548X
or with Ethernet chip that can be integrated to CAN Transceiver chip
-> "Ethernet for Automotive('')":https://www.nxp.com/products/interfaces/in-vehicle-network/ethernet:MC_1436432488692
Hope it helps.
Best,
Neil