I just pulled the manuls for all three of them, may be in luck - they all seem to run NMEA2000 if you believe the sales leaflet, but read on....
It looks like Garmin have taken the opposite view to Lowrance and you don't get the NMEA 2K cables included so you may need to go shopping, andyou can then literlaly "plug'n'play as per
Page 8 of the PDF. The "other devices" are your VHF & your Fishfinder.
Now, assuming you donl' want to go out & buy a load of NMEA cables & Ts, based on
Plotter to VHF
Plotter Black to VHF Black (also doubles as VHF power -ve by the looks of things)
Plotter Blue to VHF Purple
Plotter Brown to VHF Blue
Fishfinder to Plotter
I am now confused. Pulled the manual for the fishfinder,
only to find no mention of NMEA2k, even having seen it talked about in the sales bumff!
If I am reading this right, you might be better building an NMEA2K network between plotter & VHF, then connect the fishfinder to the plotter using the 0183 wires thus:
Plotter Black to Fishfinder Black
Plotter Brown to Fishfinder Blue
2k is certainly the easier way to go, however check your plotter manual for a 2K port - I may have dug up an older version of your fishfinder.