Importing Audi from Canada

[RJA]

Does anyone know the exact procedure and requirements for importing an S4/6
from Canada?  Car is Canadian spec.  Does the speedometer need to be
modified?  Any other mods required?  Is some sort of certificate of
compliance required from Audi?  Are there import duties or taxes required?
How does one drive it across the border?

Looking for a clean, low-mileage S4 or S6...  doesn't have to be Candian!

-- Rich
   '90 Audi 200
   '83 Coupe GT