Just an FYI, the first link (NMEA OneNet) sounds great, but isn't actually used by any of the major manufacturers yet sadly.
Also, only NMEA2000 is based on CANbus, NMEA0183 is not.
Also, only NMEA2000 is based on CANbus, NMEA0183 is not.
NMEA2000 is essentially a Marine Electronics version of CANBUS with their own agreed upon PGNs.
NMEA0183 is pretty close to RS-232 (and/or RS-422), usually at 4800 baud, but there's a "High Speed" variant at 38,400 baud.