I could see Bell MTS not supporting the unit. They still have their own purchasing and inventory systems although they use Bell's purchasing power for the items they do carry. They wouldn't have any trained installers.
I was thinking you could call Bell directly to see if they can provide the service in your area, since they now use the same towers as MTS. I don't know how the outdoor unit is connected, so that may also be an issue.
I've got to wonder if these routers will work like some phones. It's often possible to take a phone SIM and put it into another phone and have it work. If that's the case, it might be possible to get a SIM for a phone or tablet data plan and just insert the SIM into a third party LTE internet receiver. Even if the router has to be registered on the network, the system may accept it as an ordinary LTE phone or tablet device.