We did this recently and here is the process we went through:
-Make sure your vehicle is admissible (visit the RIV's website or Transport Canada)
-Get a recall clearance letter from the manufacturer or the dealer (on proper letterhead) and fax it to the RIV OR just use a service such as recallletters dot com to do this on your behalf (I did). This letter is valid for 30 days only. There can be no outstanding recalls on any vehicle you want to bring to Canada. Follow-up with the RIV in a few days to make sure they received the letter.
-Notify US customs at least 72 hours in advance that you plan to export. The car must be in the US during this time. We did it crossing from New York into Ontario. The Lewiston Bridge is the only bridge you can export a car from the U.S via New York to Ontario and you must do so during business hours (8 to 4 M-F ONLY) In the case of the Lewiston bridge US CBP will request that you send them the VIN number by e-mail, again being sure to give at least 72 hours notice. The US CBP website has the details of what is expected by the crossing you're going to (fax or e-mail and operating hours for vehicle exports)
-Be sure you have valid insurance coverage for driving your vehicle from the US to Canada and from Canada to your home.
-Appear at the US CBP vehicle export office with your title, a copy of the e-mail you sent (with their acknowledgement of receipt), and any other relevant documentation. Once they've cleared your vehicle for export they will stamp the title.
-You must then go to the Canadian side and declare your intent to import your vehicle. They will make you fill out Form 1 which they will stamp once complete. Once this is done and they've cleared you you must go to the cashier and get a receipt showing that you paid duty/taxes (or that you paid none as none was owing)
-The RIV needs to see Form 1 to issue you Form 2. We went to the RIV head office on the West Mall in Toronto rather than wait around for things in the mail. We also made our payment ($200-something) at that time. Some people say Customs Canada will collect the fee on behalf of the RIV but this was not the case, the cashier at the border didn't take the payment for the RIV fee.
-We exchanged the US DL for an Ontario one at this point. They will keep your US licence and issue you a temporary paper one without a picture until you get the card in the mail. Also arranged for Canadian insurance as soon as we got home from the licence office. We did not cancel the American insurance until we got a confirmation of insurance e-mail with the policy details from the local insurance company. Print this and keep it in the vehicle until you get the pink interprovincial liability card in the mail.
-The Form 2 you will take to the designated inspection centre nearest to you (usually a Canadian Tire) and they will do the RIV inspection at no charge. We didn't have to have any modifications done as the vehicle already had daytime running lights, metric speeds on the odometer (under the miles) and child seat tethers. Once passed they're supposed to fax Form 2 to the RIV* You must also get a provincial safety certificate, and in the case of Ontario a "Drive Clean" emissions test done. You do not have to do these last two things done at Canadian Tire but we chose to do so rather than drive somewhere else and wait again. They will also stamp the Form 1
-Take Form 1 stamped by Customs Canada and the inspection centre, the safety certificate, the Drive Clean results, the original US title (stamped showing as having been exported from the USA), your new DL, proof of local insurance *AND* the receipt showing duty/taxes paid upon import (didn't think to bring this one at all and just happened to have it in the same folder) to get provincial plates. They will keep the state title at this time and issue an Ontario one to you. Bring your passport since your new DL doesn't have your picture (yet)
-Check the RIV site for an update on your case every few days. Ours kept showing "your form 2 is ready to print" in spite of the fact that we had already passed the federal inspection. We called the RIV who insisted they never got a fax from Canadian Tire. Drove down to the Canadian Tire and it turned out the Form 2 was just sitting in some pile
and hadn't been faxed. The guy promised he would fax it in a minute. The next day the RIV case status was updated to reflect this.
-Get a compliance label from the RIV in the mail (they give you instructions on where to put it)
-Advise your former state of residence to cancel your vehicle registration.