[911Rob]

Hey Shinrai,
I've brought cars from AB to BC, so it's similar. It's all posted here, but to summarize:

First contact your Motor Vehicle Branch where you'll be registering the car.
Tell them what you are doing and they will tell you what you need.
Find out about plates/insurance for the transferring process too?

So you buy the car in AB.
If it's from a dealer they will charge you GST.
You put your temporary plates/registration papers on the car and transfer to ON.
There you will have to use an accredited mechanics shop to inspect the car and certify its safety and use for your Province. Keep in mind that ANYTHING they find wrong with it MUST be fixed and they can be fussy! Little things like a door hinge that allows the door to drop 1/4" must be fixed, exhaust systems, suspension systems, motor, lights, etc. must all be working or repaired to get certified. You might want to "ask around" for a shop that isn't too critical?
Then if the vehicle is a certain date (per exc911ence) of age, you'll need a written appraisal to verify the value of the car. When you go to register it, you'll be charged the Provincial Sales Tax (PST) on the value of the vehicle. Some MVBs are fussy about insuring cars too old and require additional safety inspections? (AB does this), depends on insurer, so check that too.
When they register it, they'll check to make sure the last known registrant was the person that sold you the car; I'm not sure what happens if it isn't, but its a safety check against car theft of some sort?

All in all, it can be costly and there are unkowns that can drive up the budget; so be careful and good luck.