I recently looked into this as well, and while it does seem like a lot of hoop jumping at first, once you get it all sorted out it isn't really that bad.
Unfortunately, for the vehicle I was interested in, there was no guarantee that the US warranty would be honoured in Canada, so I ended up buying here at home.
For Nissan, the vehicle must have been registered in the States for 6 months before export, this is the manufacturers way of making it more difficult to purchase brand new cars down south. Toyota though, will honor warranty on brand new cars. GM dealers get a good smack around for doing it, but then, who would want one. The tricky bit is to get the PAPER copy of the original title as Warshinton has electronic titles, so you have to ensure that the dealer gets it from Olympia. You need to fax a copy of the title, a bill of sale, and an export from to the US border services at least three days before you export, and have the originals when you cross and your are pretty well done. There are a few small hoops to jump here with a federal safety inspection at Canadian Tire who will want to see Daytime running lights and car seat anchours, then you are on your way, with five or six grand in your pocket to buy up waterfront property on lake washington that will be up for grabs soon.