in Ontario if your vehicle & trailer rgvw is over 4500kg, or 10,000 lbs you need to get annual inspections
if your trailer is rated for(or more than ) 4500kg ( 10,000 lbs) you need an A license. G class won't suffice .
trailers up to ( I forget the number but I think 7,000 lbs) lbs are weighed at the wheels only, not including the tongue weight. over that weight the entire trailer is weighed ( including tongue weight)
yet any camper , rv etc doesn't play by the same rules
EDIT I stand corrected.
If the trailer weighs more than 2,800 kg (6,171 lb.); Register the truck for at least the combined weight of the truck and trailer
If the trailer weighs 2,800 kg (6,171 lb.) or less; Register the truck for at least the weight of the truck , which includes trailer tongue weight. Weight transmitted directly to the ground, by the trailer, is not included in the RGW.