I did the vice-versa- my Garmin feeds my Smartcraft- GPS speed, sonar depth finder and waypoint distance with fuel burn/time, time of day, etc.
With most of them NMEA 2000, I wouldn't think it would be a major task. Install/wiring diagram would be all that is needed- I did a few connections myself who, on a 1-10 scale of tool related work I'm a 2 at best. Color coated wires = pretty simple.