Where in Canada are you? I'm in n. BC. Is your house insulated? Do you have a pond for them? How do you keep them in winter? I've been contemplating whether to keep water open for them, but I can imagine the heating bills would be astronomical.
A livestock tank heater shouldn't cost a lot.. i have one for the horses and i know there are floating types... it runs for months end in winter i see no adverse effects on my hydro bill, they are thermostatically controlled.