Fastest way to get rallying:
Read the cars rulebook here:
http://www.carsrally.ca/index.php?option=com_content&view=category&id=15&Itemid=...Once you've read through that you'll need to conform to the rules for the class you plan to enter. My guess is Production 4WD (The cheapest way to start)
So you'll need to get a roll cage installed. Plenty of people to contact for that. Few names that jump out:
Ryan Huber - Rally/Race Developments
Frank+Dan Sprongl - Four Star Motorsport
Ronnie O'Brien - O'Brien Motorsports
Stewart Hoo - Canjam Motorsports
You'll then need safety equipment:
Helmet that conforms to the CARS rules
Hans Device that conforms to the CARS rules
Fire Proof race suit that conforms to the CARS rules
Wheels that can handle the abuse that the WRX can give it. (Speedline, Method, Compomotive)
Gravel Tires (Pirelli, DMack, Kumho, Yokohama)
- You'll require a compound of gravel tire that suits the temperatures you will be running in.
Rally Suspension (This really depends on your budget, endless manufacturers out there. Some that come to mind quick are: Hotbits (Peter Reilly) RSSP, Proflex, Reiger, lot's of other ones out there)
Brakes to fit under the rally wheels (2006-2007 WRX 4pot 2pot brakes fit)
Skid Plate
Rear Diff Protector
32mm or 34mm turbo inlet restrictor (Which then has to be sealed by a CARS representative)
Intercom (Peltor, Stilo or Terratrip make good ones)
Or.........
You can just go the cheaper route and buy a car already built:
http://www.mlrc.ca/cgi-bin/yabb/YaBB.pl?num=1429982434My personal tip to you:
Start off slow and don't try to run before you can walk. Lot's of people start out with powerful cars and end up crashing in their first few events never to be seen again. Nobody will judge you if you're at the back of the pack for the first few events. Seat time is the only way you will be fast.
Once you start you won't be able to stop!

Come on out to the MLRC rallycross or the KWRC rallycross which doesn't require much at all other than a few $, a helmet and a car that drives. You'll meet a bunch of people and get to drive on a closed course.
All the best with the build.