Just had a chat with all three involved parties; CBSA (custom), RIV (registrar of imported vehicles) and Transport Canada.
Heres the scoop and it's pretty straight forward:
If the vehicle has been modified and is less than 15 yrs old you're out of luck, they simply won't let you re-enter Canada.
If the vehicle is over 15 yrs old both Transport Canada and RIV are no longer involved. So it's all about CBSA who will require you to re-import your vehicle and pay duties on the new value of the vehicle.
So let's say you bought your 15 yrs old van for $10,000 in Canada, drove down the states to get a new rooftop and 4x4 conversion (now valued at $25,000) then go back to Canada. You will pay duties on $25,000 regardless if you already paid taxes the initial $10,000 purchase price. Given that it's an older vehicle but a "new" importation you won't need a federal inspection, just a provincial one.
Now how do they value your "new" vehicle I'm not sure but at the end of the day it can be done
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