You can’t, because it is not yet available in Canada (at least as I write this). It’s a feature that is only available on the Apple Watch Series 4, and when it is turned on in Canada it will be available through the Heart Rate app.
The technology has been approved by health Canada, we’re waiting on Apple to activate it. At this point, I’m beginning to believe that it will not be available here until the release of the next version of watchOS, in September. It could come sooner, however.