Couple of months back I flew to Florida and bought an SRT6 and drove it back home to Ottawa. Process is simple.
1-register with RIV $195 (Registry of Imported Vehicles-Transport Canada) and they will inform you of requirement of the vehicle to be legal in Canada in Crossfire case it will require Daytime running lights only (get the $45 kit from Canadian tire...easy install but you will have a warning light of the lights on)
2- buy the car and ask for a bill of sale from the seller (you will be required to produce it when registering the car in Canada
3- go to the nearest DMV with the seller and transfer he car to you (title=registration)
4-pay the state taxes (Florida=6%) at the DMV
5-buy temp plate at the DMV
6-call your ins co. and get car temporarily covered ( you should discuss your purchase with them prior to heading to the US)
7-***most important part*** you must send your new ORIGINAL title to the US Border/customs that you will cross 3 DAYS PRIOR to your arrival so they can verify vehicle is legit and not stolen etc...keep photocopies of the title in case you need to produce them to police (speeding lol)
8- Take 3 days to get to the US customs border you sent your title to and report in. You will be ask only a few question they will check the paperwork and the VIN on the car and then you cross over to the Canadian customs and also report in to get paperwork done...RIV Title Insurance... You will need to produce all of the above info to them and YES you will pay the GST on the spot.
9-fix your car so it is legal for the RIV standard...daytime running light in the case of a Crossfire...different for every car
10- bring your car to Canadian Tire for them to sign off and stamp the RIV (this is the only place Transport Canada has authorized to do this...oh its N/C free since you already paid your $195 RIV fee in advance.
11-get Etest and Safety check
12-go with ALL your paperwork from the bill of sale to the safety check to get your car plates and pay the PST as you would any car.
13-Call your insurance and have fun...

Paul