I don't know about in Canada, but in the US there are Mercedes car dealers and Mercedes van dealers. Most van dealers do cohabitate with a car dealer (but not all) but only, iirc, about 2/3rds of car dealers have a van dealer.
The car-only dealers are not authorized to sell, service, or repair vans. Also remember that in the US, with a few controversial exceptions (e.g. Tesla) not only are car dealers not owned by the manufacturer, but it is illegal for them to be so. It is also illegal for them to set prices for the sale, service, and repair of said cars and their parts. That's why it's called MSRP or "Manufacturers *Suggested* Retail Price".
Most of the car only dealers don't sell vans by choice. In their opinion Mercedes should not be selling commercial vehicles in the US, and certainly not at a vaguely competitive price. They would, in fact, prefer the whole venture failed- or at least got rebadged as freightliners permanently.
So a car only dealer refusing to service it isn't surprising.