living onboard in Toronto requires serious heat
I am from Toronto although I am living onboard in NYC now. For what it is worth I owned a Niagara 35 Mk 1 for several years. We have propane cooking and an Espar for heating and has worked out really well. During the winter we burn 25 to 50% kerosene depending on the temperatures. The Espar dealer suggested this would help keep the burner clean. We buy our diesel at a truck stop since it is much cheaper than at the marina. Filling from those no-spill jerry cans has worked really well. Interestingly, the nearest propane station is right next to the truck stop so it would be the same distance for either.
A comment about the Niagara. Most were built with a Paloma propane water heater (I have intention about starting a fight about these!). The Paloma worked well for me for years but it does mean that you will be using propane in any case (and turning off the unit when not in use).
As someone else said, do not buy a boat based on what heating system it has. Buy the best boat for living aboard and cruising and modify it to meet your needs. If a boat has a propane heater try it out in combination with electric heat. I would not rely on an unvented heater though for overwintering as condensation is already a big enough problem without adding to the moisture content by heating.
Diesel heaters (other than stoves as in BC) and bulkhead models either use hot air or hot water to heat the boat. The former have quite large air ducts and you would have to route them carefully to heat the whole boat. On a N35/mk 1 you could place the heater at the aft end of a cockpit locker which would be great for the exhaust piping but it might be quite hard to get a hot air duct into the main cabin (might work on the portside through the galley above the refrigerator. Hot water heaters (hydronic) have much smaller pipes and can provide domestic hotwater too, but are even more pricy.