I imported my dream spec 335i from Canada. It's best to have a company do it for you as it's not as simple as just driving it through. Here's the steps I took and it was pretty hassle free:
1. Look up a list of all NHTSA importers. The list can be found here:
https://www.nhtsa.gov/sites/nhtsa.do...ust_2_2018.pdf
2. Decide which to go with. Most I talked to were rude, unwilling, didn't know what they were doing, or were no longer in business. I finally found one in New York which worked out great since my car was in Ontario. It was called Superior Auto. Highly recommend them if your car is on that side of Canada.
3. Contact BMWNA for a letter of compliance. They got back with me in about 24 hours with the signed letter containing the VIN of the vehicle.
4. Send that letter to the import company along with the VIN sticker from the door frame from the car. Seller of my car was cool and willing to get any pics I needed.
5. Buy the car and arrange pickup.
6. The import company will pick the car up and I just had mine shipped through them all the way home. Total cost was around $3,500 if I recall correctly but it was well worth it.
Hope this helps!