We bought Sherman (our motorhome...he drives like a tank!) in New York State.
When we started shopping, I quickly noticed that prices in the U.S. were much lower than prices in Canada. How much lower? Well it depends somewhat on how much money you're planning on spending, but I'll use our experience with Sherman to give you a real life example.
In August of 2007, we paid $12,500 U.S. for a 28 ft Damon Daybreak Class A 454 Chev chassis with 25,000 miles (40k km's) on it. The exchange rate at the time was similar to what it is now, and so it cost us $13,083.51 CAN. But there are other costs involved with bringing it to Canada.
When you buy a used vehicle privately in Canada, you only have to pay provincial sales tax, not the GST. But when you import a used vehicle, you have to pay both taxes. So with Sherman, we had to pay $1,041.98 for Ontario Provincial Sales Tax, and $781.49 for GST. Also had to pay $100 CAN for Air Conditioning tax.
You have to go through the Registrar of Imported Vehicles to make the procedure official. They charged us $206.70 CAN for the processing. Their website is also full of all the information and steps you need to follow in order to complete things without any headaches.
We had to provide a recall search letter from GM regarding the chassis, and from the manufacturer regarding the motorhome itself. Damon gave us one for free, but GM charged us $26 CAN.
Finally, we had to have the headlight system adapted to operate as daytime running lights to conform with Canadian law. This cost $200 CAN.
So in total, we paid $15,439.68 CAN.
The very best deal we saw at the time on a similar vehicle in Canada was over $20,000 CAN. However, it's a much simpler procedure, and your only other cost on top of that would be Provinicial Sales Tax of $1,600 CAN.
So we figured we saved at least $6,160.32 by buying in the U.S. and importing into Canada.
Now, we bought an inexpensive used RV, and it was definitely worth the extra time and effort to go through the procedure. A more expensive unit will make the process even more worthwhile.