It's not Canada Post's fault any more than the horse+buggy industry was responsible for its own demise. A long time ago, "snail mail" was the only way for the average person to communicate with distant relatives. Long distance phone calls were horrendously expensive.
Flash forward to today. Many cellphone plans have a "free cross-country-calling" option. Video calls are commonplace. And of course email happened. Why pay for a stamp and envelope for a letter that'll take days to show up, when you can send a free email that'll show up in the recipient's inbox in minutes?
Face it "snail mail", and Canada Post in general, is doomed, just like the horse+buggy before it, and legacy Pay-TV now.