Depending on the population you're looking at, the country you're looking at, and the definition of mental illness or mental disorder, the figures range from 5% to 70% within the literature. And that is not just within a Canadian context.
Meta-analysis has generally ballparked the number from reviewing international studies at around 8% to 12%. I can't provide you with the inclusion criteria for how they defined mental illness within that 8% to 12%, but I can certainly provide research references for that.