I believe that I was in touch with the places noted above in TO and Mississauga, and was told I required the collar and a valid pressure test stamp. The automotive places in Kingston refused to fill anything for me that wasn't part of a car.
For all the grief required, and travel, and inconvenience when you run out, the cost of switching to propane is not so bad, and it improves the resale value of the boat. For my boat, the tank can be mounted under the starboard side stern cockpit seat, as it is open to the air, and satisfies the locker requirements. I re-ported my existing stove at nominal expense. The rest was the cost of 20' of hose, values, solenoids, and the trident gas detector switch panel and some time and effort to install.
Chris