Look at these from digikey:APC1760-ND $4.24waterproof O-ring and mounting nut included.
First do you use my NMEA2000 library with NMEA2000_avr?
Have you tested just listen traffic on bus by using example ActisenseListener and do you get it right?
What is your other display?
I tested with latest libraries and seem to work. Note that you should not use original Seed studio can bus shield library. MCP_16MHz has been defined in developed version of CAN_BUS_Shield library in file mcp_can_dfs.h on line 250. If you do not have that, delete your Arduino\libraries\CAN_BUS_Shield-master and download it from https://github.com/peppeve/CAN_BUS_Shield and install it.