In a nutshell, you start by exporting the car from the US and then import the vehicle to Canada. Once you complete the export and import process, you register the vehicle and get your Canadian provincial plates and title.
More specifically, the process entails the following:
1) Confirm the car is eligible
Check the riv.ca website to confirm that your car is eligible for import and to see what modifications you may need to make (e.g., daytime running lights) to pass inspection once you are in Canada. You can make the modifications either in the US or upon arrival in Canada (i.e., you don't have to do them before crossing the border but do need them to pass inspection in Canada)
2) Prep for the move
- Contact the Ministry of Transportation for your province to understand what you'll need to register your car (e.g., driver's license, insurance, import documentation, etc) and get whatever you need lined up. For example, Ontario requires an Ontario driver's license to be able to register the car, so make sure you have everything you need with you to get it (e.g., for some states you may need a driver history). Ditto for Canadian car insurance.
- Get the recall clearance letter. Specifics here depend on the car manufacturer (e.g., Toyota provides the information on their website; Honda is similar but requires registration on their owner's website; some other brands require specific requests). Send the letter showing no outstanding recalls to the RIV (document is valid for 30 day) to support @ support.riv.ca so they pre-process it. Call them to confirm all's set before you leave the US so you can get anything else necessary before you leave.
- Confirm your US insurance will cover you in Canada and get a letter of experience to help you get Canadian insurance
- Lay foundation to get insurance in Canada (you'll need it to register your car)
- If you don't own the car (e.g., you have a lease or loan), get authorization to export the car from the lienholder
- Make sure you have your car title easily available
4) Export car from the US
You can only export the car at certain border posts in the US and at certain times. So, decide where you are crossing and then understand that specific border post's requirements. Border posts are usually looking to get the required information 3 (sometimes natural, sometimes business) days before you arrive at the border. Take a look at http://www.ucanimport.com/Border_Crossing_Info.aspx for a good list of border crossings, but then search for the specific info for the border post and their instructions on the CBP website directly. For example, for Buffalo, look at http://www.cbp.gov/xp/cgov/toolbox/contacts/ports/ny/0901.xml and search "export a vehicle" to see an example of the instructions (other crossings sometimes need you to mail them the title so they receive it 3 business days prior so it's important to check for your specifics). You can search for other border crossings at http://www.cbp.gov/xp/cgov/toolbox/contacts/ports/ . Find out the location of the export office online or when you call them (it's not necessarily easy to find when you are at the border).
On the day of the crossing, stop by the CBP export office before you cross the border into Canada so they stamp your title to clear it for export. That stamp will be verified both when you import the car into Canada and then when you register the car.
3) Import the car into Canada
After you cross the border, tell the officer you are importing the car. Show them the stamped title and they'll send you inside to complete the process. Fill out the document at the Canadian border post - one page with your name, address, etc and car info. You'll need to get Form 1. If your car is included on your B4 (either submitted that day or previously), your tax rate will be 0% but make sure you keep the receipt carefully ... you'll need it at the Ministry of Transportation. Include your e-mail on Form 1 so the RIV e-mail you Form 2 (faster than mailing it). CBSA will be faxing Form 1 to the RIV.
4) Pay the import fee to the RIV and get your Form 2 from the RIV
You'll need to pay $195.00 + GST/HST (or QST) either at riv.com or by calling the RIV at 1-888-848-8240 (Mon. to Fri.: 7:00 a.m. to 12:00 midnight (EST), Sat. and Sun.: 7:00 a.m. to 5:00 p.m. (EST))
You'll need the red numbers from your Form 1 to do this step and they will then e-mail you Form 2 which you'll need to get the car inspected.
5) Get your car inspected for import inspection (at Canadian Tire) and, if necessary, provincial inspection
You'll need to get your car inspected to ensure it meets Canadian standards (remember the checklist you got at the beginning from riv.ca ... they'll check for those modifications so get them done before elsewhere or arrange to have them done at Canadian Tire). The cost is included in the import fee you paid to the RIV. Plan for an hour or hour and a half for the inspection.
Depending on the province, you may need a provincial inspection too. For expediency, you may want to have the provincial inspection done at Canadian Tire the same day. Just tell them when you make the appointment so they can schedule it in.
Canadian Tire will stamp Form 2, which you'll need at the Ministry of Transportation. Make sure they fax the form to the RIV so the system shows you passed the inspection.
6) Register your car and get plates at the Ministry of Transportation
The specifics vary by province
7) Cancel your US insurance and send your US plates back if your state requires them
8) Celebrate!!!
I have a scanned copy of my passport on my phone and work computer so the second we get the email requesting it I can reply with it in minutes. Not that it will probably make much difference, but for my own piece of mind. Also am paying my RPRF next week since I read it can take awhile to get that matched up to the file. 
