Schools have an internal selection process, I got an email when they forwarded my application to NSERC. My application shows "Received" on the NSERC website.
So my university sent an email saying the results will be released April 15th. But they also said "Vanier Canada Scholarships and Tri-council PhD results will be announced once the agency has provided an updated timeline".
So I don't know if they actually know the release date or just basing it off the mid-April autoreply email from NSERC