Simple economics, the U.S. have a much larger consumer base.  Both Coke and Pepsi have offered several different Diet Colas over the last few years, and most of them are no longer available due to poor sales.  If Canadians truly wanted Diet Cherry Coke, it would be available.  Remember Black Cherry Vanilla Diet Coke?  I personally loved it, but I guess the majority of us didn't!

The manufacturing of a can of coke is vastly different then the shifting of bits (service). You compare apples to oranges.