Yes you will be having some headaches... I too wanted to import a new car into Vancouver for my Grandmother to drive, since her old ford jalopy was rusted out...
She did all the motor vehicle research on getting it through, only to conclude it's easier to buy in Canada.

If your close to the boarder, I would try and get a mailing address in Washington, and have the car registered there if your in BC area, or any other US state nearby, Heck maybe you can buy a small cheap lot on the US side for $10,000 and just post a mailbox on it. You could probably make a business out of it for other poor Canadians, charge like $400 for the year to register their cars there, I'm sure my grandmother would go for it.

As for converting to Canadian specs, the initial cost may be recouped when you sell the car. Why are you buying it in the States anyways? Does not DC have a dealership there?