I have actually recently registered my US-registered car in Canada. I was living in Michigan and had to leave and wanted to move my car to Ontario, Canada. I had it registered in my father's name because I don't yet have any status in Canada.
Basically you will have to contact an import agent. They will do all the paperwork for you and ask you to fax over required documentation (VIN number, registration, title, recall letters, value, etc.). The agent's fee was about $250.00
You will need to get your car valued at a dealer. But because I was "selling" the car to my dad, I just put a sale price and printed out a bill of sale. I listed my 2003 Mazda 6 for $6500.00 even though it was valued at about $9500 at that time. You will need to pay a fee to the agent, and a number of taxes, including GST. If your car wasn't made in North America (VIN numbers starting with 1), then there is an additional tax. The GST and other charges amounted to about $800.00, paid to the Agent, so I ended up paying the agent a little over $1000.
If your car is already in Canada, regulations require you to bring it to the US for 72 hours. When you bring your car from Canada to the US, you will have to let your title be stamped by the US Customs to prove that you are bringing it out of Canada for the required amount of time.
When you bring your car into Canada from the US, you will have to tell the customs officer that you are importing the car and he will redirect you to an office where all the import agents are and they will stamp your registration there and give you a few forms required to register your car in Canada.
You will need to have an address in Canada to put on the registration. Since I was passing the car to my father, I didn't have to pay any PST because there was some rule in Ontario about not taxing if you are passing a vehicle to a relative.
If your car doesn't have daytime running lights, it is mandatory to have them installed if importing them to Canada and they will make you do it before they give you the registration. That cost me another $400 at Mazda Canada.
Basically all in all, if your car is old and/or worth less than $5000, sell it off and get a new one in Canada because all the taxes and fees will cost almost as much as the car and it is simply not worth the trouble. If you have a relative in Canada to register it to you can avoid the Provincial Sales Tax and probably undervalue your car to avoid paying as much taxes. There is a ton of paperwork and a ton of running around.
Canadian insurance companies will not insure a car with a US registration and vice versa. I believe that if your car is going to remain in Canada for more than a few months (not sure of the actual time period), you are required to register it there. Even if you keep your US registration and insurance and you get into an accident in Canada
If you get US driving record from the state you live in you can greatly reduce your insurance rates. When I first got my Ontario drivers' license, they quoted me $400 a month based on having no driving history. But when I showed them my driving record and "no claim" record from my insurance company from the US printed out by the State of Michigan, it was reduced to $120, and it is about $100 now because I've been with them for a while. I also put my name on the insurance of my brother's car (he's newly licensed with no driving experience and he had an accident that was his fault) and it brought his insurance down from $600 a month to about $300 a month.
