"why can they be honest?"
What would you expect Shippo to say? It is the middle-man in this scenario, they don't have a hand on the steering wheel at Canada Post. The problem doesn't affect every level of service that Canada Post is offering, my shipments were still being accepted at the postal counter this morning and I watched other people buy certain kinds of postage service in front of me. The worker had to think creatively, however, to get things to work and had to forgo certain options that should normally be available.
In short, Shippo told you what they know. They can't peer into Canada Post's infrastructure and give you a more specific estimate of how many users are affected and which users are affected.
