Google can be your friend for such questions!!!
Basically, the answer is "NO", but then there are the "maybe" "ifs" and possible hacks.
Maybe start here:
does Apple watch ECG function work in all countries
, or add/change in Canada
Then some hits:
Changing Your Apple Watch or iPhone's Region Won't Enable ECG App Outside of United States
Thursday December 6, 2018 11:00 am PST by Joe Rossignol
How to Get ECG on Apple Watch Series 4 Outside U.S.
That should get you started...
But you might want to have it working when you hit the Customs on your way back. At least they are close to the borderline...
And PS: The Canadian hospitalization treatment is a hell of a lot cheaper... so make sure you get to one of them from the Customs border point if the Apple watch does happen to go off... and it's still in range and working... ;-)
Actually, this looks a bit interesting:
You Can Use Apple Watch Series 4 ECG in Canada with US Region Workaround
BY CHRISTOPHER BAUGH – 5 MONTHS AGO1010
Heck, why does it have to be "approved" for use in Canada when the user will probably only be using it as a guide and/or whether to get to a hospital or clinic or not???