Your house is probably heated by a gas furnace... Many houses are heated by gas furnaces still, but a lot of people want to upgrade to electrical heatpumps these days to be green. A typical 2000sqft house in Ontario (with decent insulation) needs 50,000 btu heating or 15kw, usually at 240v, so thats 60A to heat the house with an air-air heatpump. Even geothermal would need around 30-40A. Heating takes a LOT of energy in Canada.

If the house has a 100A service and it's electric heating, then you have 60A heating, 20A hot water tank, 30A oven, 30A clothes dryer, 30A car, and other appliances/etc (fridge, freezer etc) 30A. That's 200A. You can't just shut off the heat or hot water tank, so the hwt will be tripping the breaker when the car is charging and the heat comes on, you'll have to run your dryer when the oven and heat are off... see the problem?

Typically on a new house the panel AND service are sized for estimated TOTAL equipment. Installing double the capacity of the service isn't considered good engineering practice.