Seems to be yet another mail product which evaluates your email and sells info based on it to advertisers. They say they use " anonymized and aggregated data" but they also note in their privacy policy that they use and send data to Google analytics and Facebook analytics, and on iOS they use the AppsFlyer service, which collects and “analyzes users’ IP addresses, device information, and IDFA” - your advertising ID(!). Even if you stop using Canary, “data collected by third-party vendors such as Google Analytics may remain with them as per their data processing policies”
I took a quick dive into the Indian company that owns Canary, Mailr Tech. Their headquarters address (7 Jagnath Plot RAJKOT Rajkot - 360001 Gujarat - India) is shared by 1955 other companies, so it’s basically a mail drop. Did a quick search on LinkedIn to see that devs there might be doing and found this:
“textual data… make data business usable… learning sentiments”
This seems like the same thing that Edison Mail was caught doing: scraping user mail to sell info on what people subscribed to, what people bought, and from what stores, and at what prices, etc etc.
One of the three limited partners in the company also owns ACE NATURE CURE LLP. 
I’m pretty conservative about how I use and access my email, and who gets to see it, so I think I’m going to take a pass on this.