Your insurance company will have a questionaire that will need to be filled out in order to properly assess. In Ontario, many factors can contribute to a rated premium including amount of liability coverage, presence of older, knob and tube wiring or alluminum wiring, size of electrical service, age of roof, square footage of home, whether the home is heated by oil, presence of older style plumbing - like galvanized pipes and cast iron drains - and most importatly, the cost to re-build.
As such, its really tough to ball park an estimate - especially on an older home.