Canadian Government Open Data.
Open Government, Canada API is a free Government API that requires no API key, is only available over HTTP and has unconfirmed CORS support.
Collaborative open source project led by the Government of Canada
Details from open.canada.ca.

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The Open Government, Canada API is provided by Government of Canada (open.canada.ca). Collaborative open source project led by the Government of Canada
Yes. The Open Government, Canada API is listed in the Government category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Open Government, Canada API requires no authentication, so you can start making requests without signing up.
CORS support for the Open Government, Canada API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
No. The Open Government, Canada API is only available over plain HTTP, which browsers block on HTTPS sites. Call it from a server instead.