A D license is for bigger trucks, not trailers.  A Class D is not about towing a larger, heavier trailer; it is about larger and heavier tow vehicles.  Ontario Highway Traffic Act states a Class D driver can drive “Any truck or motor vehicle combination exceeding 11,000 kg provided the towed vehicle is not over 4,600 kg” This means, if the truck is over 11,000 kg you can drive it.

If the truck and trailer is more then 11,000 kg combined you can drive it;  unless the trailer itself is over 4,600 kg.  You’re limited to a towed vehicle(s) of less then 4,600 kg. It is the exact same limit as your Class G license!

Class D license holders may also drive a vehicle in Class G.