I would assume if they were stolen the original RO would have filed a police report which goes nationwide once filed so the RCMP should be able to contact the last RO at least. Not sure how it works with insurance companies if they become the owner once they pay it out but I would assume the RCMP would inform them at the very least. Unless the sled was never registered or insured after purchase it should be able to be traced back to the last owner. Even if it was sold to someone as used who never registered or insured it and never reported it they would be able to trace it back to the last RO on file. In which case if that person did sell it, they better hope they kept the bill of sale so they don't get dinged with the littering fine or recovery cost.
Sounds like life would be so much easier for everyone if folks just registered their sh!t instead of trying to skirt the govt and worrying about the $75/yr.......