From my perspective as a child of the 70s in a province not on the US Canada has been flooded with US culture.
At worst in my childhood were maybe a McDonalds and a Dairy Queen. No cable TV and few other cultural influences.
Now we're fat, WalMart shopping, gun toting, rap music/urban culture, even dialects are more US sounding.
My childhood exposure of Canada was through the movie strange brew. Still a favorite of mine.
http://www.imdb.com/title/tt0086373/
I figured all Canadians were hosers who scarfed donuts and drank beer.
Then I watched Kids In the Hall and I figured they were mostly funny gay fellows.
Then I watched South Park . . .
South Park is the most honest portrayal of Canada in the media today.
The US and Canada are not the same country, but they're similar in a lot of ways. If Canada's graph shows the same drop, it'd be an indication that maybe the problem isn't with the US healthcare system, maybe it's something about culture/diet/environment/etc.