It appears that the Apple Watch Series 4 ECG app is about to hit Watches in Canada. The Health Canada database show the ECG and irregular heart rate rhythm notifications as being approved as of the 16th May.
With the approval, Apple should soon be enabling the ECG feature in Canada, perhaps in an upcoming iOS 12.4 and watchOS 5.3 public update.
Although every Apple Watch Series 4 wearable ships with the ECG hardware, the feature must be enabled on a country-by-country basis. Apple must receive regulatory approval in each country before turning on the electrocardiogram feature.
Apple recently added new countries to the list of countries where the ECG feature is available, adding Croatia, Czech Republic, Iceland, Poland and Slovakia with the release of watchOS 5.2.