Why did you make a contract when you didn't know if you'd stay?
Most likely nothing much will happen except that you get a bad credit rating. Most debts in Canada are written off after 6 years unless possibly there was some kind of fraud involved like getting an expensive phone on a 3 yr. contract and then skipping the country as soon as you got it.
That said, not paying your debts is dishonest. Talk to the provider about cancelling early. You will have to pay a fee but you will leave Canada without debt and with a clear conscience.