First, locked phones are a thing of the past. Effective December 1, 2017, service providers will have to offer unlocked devices to their customers.
What are the benefits of having an unlocked device?
An unlocked device can be used on other networks, which means that you will be able to switch providers and keep the same phone. That means more flexibility for you, the consumer.
https://crtc.gc.ca/eng/contact/phone/q19.htm
Canada:
I want to reiterate this. Even second hand phones. Find the carrier and call them. They legally have to oblige.