Hi Michel,
It may be possible (there was/is one recently for sale in the Montreal area), but I think it's difficult. The main problem is that SMB
usually starts with an incomplete vehicle (and thus an incomplete VIN) from Ford, Chevy, MB, etc. After they convert the van, SMB then completes the VIN. The Registrar of Imported Vehicles (RIV) in Canada doesn't recognize these SMB-completed VINs as importable vehicles - there is an extensive list (see here:
https://www.riv.ca/VehicleAdmissibility.aspx), including many aftermarket motorhome manufacturers, but, alas, SMB is not one of them.
However, some people purchase their vans before taking them to SMB, and therefore they would have a complete VIN identifying the vehicle as a stock van. If you are looking at used, and can find one of these, they may be easier to import. If you are looking at a new build, I would consider this approach (buy the stock van, then take it to SMB); however, I would suggest you do your research to ensure the final product is importable.
The 25-year thing that Yannick mentioned is for non-NAFTA vehicles. If the vehicle was manufactured in North America (and is on RIV's list, most are), it is a very simple process to import a stock van or any vehicle - pay PST/HST; pay a small brokerage fee; add DRL, kmh markings, English/French safety labels, and away you go. Our van was purchased in Portland as a stock cargo van, and I imported it into Canada relatively pain-free. I then had it converted by GTRV in the Vancouver area.
Hope this helps.
Brent