I went looking for the source about Canary around the usual forums, but it’s actually right under our noses.
The item that annoyed me was that they had people manually reading and reviewing emails. I left Edison for that reason (although they had other issues too).
The third-party server for Push email doesn’t affect my decision because every third party app needs to do that for Gmail (and others?).
I use Spark and my hope is that Readdle is profitable enough with their subscriptions and team offerings that they don’t need to do this advertising invasion themselves.