UK citizen- Wants to buy an RV in Canada & sell on in USA..?

You may find it way less expensive and problematic to export your own sprinter to Canada. Drive it for your six month holiday there and in the states and then ship it home from California. This will probably be easier and cheaper and more reliable then buying used, insuring, and importing from Canada to US. Plus you will be driving a vehicle you know as opposed to taking on unknowns.