I am considering a tankless, but I am told the due to our hard water in Toronto I will gte calcium build up problems.

Tankless heaters do build up a layer of mineral a bit faster than conventional heaters. However, when installed a by a pro you are set up with a manifold that makes flushing twice per year pretty easy, flush with household vinegar. You can make this even better by installing a water softner. Navien makes a tankless heater so efficient that you can vent it with PVC.