Canadian advisories (presumably from NAV CANADA) are fed into the ATCSCC system. You can see that more explicitly on the less slick version at https://www.fly.faa.gov/adv/advAdvisoryForm.jsp
Plenty of US domestic flights leave YYC every day. You clear US customs and immigration in Canada before getting on the plane so you can land at any airport in the entire country, not just international ones.