In 2013 the CRTC implemented a "Wireless Code of Conduct" which is basically "diet regulation" for mobile service providers.
This regulation states that excess data charges for roaming must not exceed $100 per month, and $50 for data overages in general (in-territory use).
This has been implemented in different ways by different carriers.
Here is the link:
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www.crtc.gc.ca/eng/info_ ··· /t13.htm