totally legal if the towing vehicle ( even vans and SUV) if they have black plates , first trailer must have tandem axles with a tongue or electric brake
, driver must be able to see the second trailer , total length not to exceed 23M.
I was through this a few summers ago with the MTO and the OPP , I was driving my full size Expedition.
Blue plates , no fine , just a warning .
I still have blue plates , I just don't tow a train anymore. .