Non-owned trailer coverage is a physical damage coverage that places collision, or "all perils" coverage on a trailer that is not owned, or registered to the policy holder. The problem is that here in Ontario we have something called "direct compensation" better known as "no fault insurance".
The gist of no fault insurance is that if two Ontario insured vehicles get into an accident in Ontario, the insurance company of each vehicle pays for their own insureds damages. For example, if you are involved in an accident where you are 0% at fault, (like if someone rear-ends you) the part of your policy that responds and compensates you on YOUR OWN policy is "direct compensation", NOT COLLISION.
It's the exact same with a commercial trailer...
If a third party smashes into your trailer (in Ontario) and you are not at fault, you are compensated out of the "no-fault insurance" part of your policy. But... what if that trailer is not on your policy because you do not own it, or, do not register it? Does your non-owned trailer coverage apply?
NO, IT DOES NOT.
The damages would be paid from the owner of the trailers auto policy under direct compensation. What if the owner of the trailer does not have it listed on a policy? THEY ARE OUT OF LUCK!
The lesson is... if you are pulling a trailer that is not listed on your policy, you need to make sure it is listed on another insurance policy. Or, make sure the owner of that trailer realizes that in some circumstances it is their own policy that would respond to an accident and not your policy.
This blog post is a matter of opinion only, you should consult a certified safety consultant to construct your / your companies safety procedures.