There are several Tornado watches and warnings in Southern Ontario. Seek shelter and ensure there are as few small projectiles as possible in your yards. You can track the weather on radar at the Weather Office, so that you can make informed decisions. Weather warnings can be found here by clicking on your region.
The site also has extensive information on storms throughout Canada as well as lightning detection, marine and aviation weather reports and forecasts.
You can also find information from other web sources like at the Weather Network, but unfortunately their servers seem to be overwhelmed when there are serious weather patterns. The CBC website also offers up-to-date information in several places and they seem to be able to handle the load with ease.