you need an MMSI number to make the emergency call button work. There are 2 ways to get one:
1. if you never boat outside US domestic waters you can get one for free from places like BoatUS. Enter your info online and it's done.
2. if you plan to go abroad (even Canada or Mexico or Bahamas) you need an international MMSI which you can get from the Coast Guard and it costs something around $160
No matter what "type" of MMSI you get your info is available to those who receive your emergency call. They then know what boat they have to look for. It is very important to fill the questions out complete when you register it and change it when you sell your boat and move the VHF over to a new one.
In an emergency the radio (with MMSI and GPS) will send out short bursts of data with your MMSI and current location until it receives an acknowledgement. Much safer and better than to try to communicate this via Ch16 reading GPS data from a screen.
The tractor GPS most likely won't work. I assume that you have a radio with NMEA0183 and not the more expensive ones with NMEA2000. You will need a GPS receiver and antenna (usually combined) which outputs the correct format in the correct method (NMEA0183 or NMEA2000). The NMEA0183 used for computer type GPS's can be made to work but I wouldn't recommend it if you don't have experience with electronics.
If you have a chart plotter with GPS it will output NMEA data you can feed into the VHF.
Ooops: just saw that you are in Canada. Sorry, don't know where you get the MMSI there for sure but this may be a start:
http://www.ic.gc.ca/eic/site/smt-gst...g/sf08138.html
Most likely some more info is also in the manual.
Edit: just downloaded the manual of your radio and it contains all the info on how to connect different GPS units (NMEA0183) to it (page 29). It also contains all the info what DSC is and how it works......