Canada Post is very constrained on what it can,and can't do, when it to rate increases.
So- they have chosen to tinker where they can- by narrowly defining the classifications for each category of mail- and then attempting to enforce those restrictions/criteria for that category of mail.
The problem in the past is far too many items have been included as LETTER POST- when by definition they items are not. And, as storage media changes, and many items are becoming smaller- the tendency for even smaller packages becoming nothing more than an "envelope" is a very real threat to the Canada Post revenue stream.
I.E. BETA CASSETTE- leads 12" Criterion DISC - back to a VHS cassette, leading to DVD, then to a memory stick, the size of a piece of chewing gum.
The trend is toward small packages.
In the US- it's been the VOLUME that has kept them going- as letter writing, and bill paying by post, all become a thing of the past. e-mail/electronic payment anyone?