I've brought an 850 in from the US back in ... 02? ... and a 780 from a friend in '08. It was a while ago, for sure, but I don't think the procedure is too different.
First, find your car. It MUST have an original title, in the name of the seller. Without this, YOU are screwed. Don't send any money until you can confirm that you have this. Do whatever due diligence you feel comfortable with: Have a local you trust take a look at it, have it brought to a shop, fly down and look at it yourself, whatever. ASK QUESTIONS - don't be Canadian and expect them to tell you everything you need to know. I've heard "yeah, I have the original title" but then when we got there the story changed to "I've been trying to get it from (whatever authority) and they said they'll get back to me, so I don't ACTUALLY have it today. I'll mail it to you, I promise". That won't fly.
If you decide to buy the car, you must jump through some hoops:
RIV: If the car is less than 15 years old it must be eligible for import.
www.riv.ca will give you all that information, and/or any modifications or certificates you'll need to secure before you can import it. Once it crosses the border and you perform the mods (if any) you then take the car to Canadian Tire and they make sure things like daytime running lights have been enabled, that you have a child seat anchor, that the speedo displays in KPH, etc. If the car is more than 15 years old you don't have to worry about any of this.
I suggest NOT driving the car back, unless you feel like a potential Roadkill road trip and feel like changing a fuel pump in the high Montana rockies. There are services that will bring your car to you, I'm sure they're more expensive than renting a pickup and trailer and driving down to haul it home. Get a full car trailer, not a dolly, and a real truck for this.
Before accepting the vehicle, have a VERY good look over it. Be sure it's clean inside and out. Crossing the border is not the right time to find out that the previous owner forgot to retrieve his assault rifle or drug paraphernalia, or that the trunk is filled with jugs of used oil. You may even want to take it to a car wash long before hitting the border to give the interior a good vacuum and a once-over.
At least 72 hours before you hit the border you must have a number of documents sent to the border crossing you plan to come across at. Not all border crossings will allow you to cross with a vehicle you're importing, so check first. From my memory you need to have a colour copy of BOTH SIDES of the original title, a copy of your insurance for the car (I imagine only if you're driving it across), and a copy of the bill of sale. When you arrive at the border you need the original copies of all these documents. Check with the border crossing - they may require more. If the car comes with a bunch of spare parts it might be a good idea to have these included on the bill of sale.
At the border crossing you'll need to pay the GST and duty of the car, plus the air conditioning tariff if the car comes with A/C (it probably will, being a US car) whether it works or not, and I believe you pay the RIV fee there as well. Both times I've come across they've made me sweat for a little while. I'm also paranoid and assume that border control has eyes on at least the last mile or so of road before the crossing.
Once you get it to Canada, you must first get the Out-Of-Country inspection done at Crappy Tire, then you need to schedule an Out-Of-Province inspection with an appropriate shop. Then the car's yours to do with as you will. I've been told to keep a copy of all the paperwork in the car if you cross the border in case anyone ever asks you questions: I'm paranoid, but that sounds a little paranoid even to me... though we still kept a copy of all the paperwork in the cars just in case.
Or you can PM solyeahman on here - he's got a 745 for sale in Saskatoon. I'm not sure how clean it is or any further details on it, but I think it's a non-turbo boring grampamobile project type thing.