Canary Mail can show you the number of unread emails in your inbox on the app icon. You can enable the Notification Badges via the device settings.
macOS
On macOS devices, you will find this in System Preferences > Notifications > Canary mail > Check Badge app icon.
iOS
On iOS, you will find this in device Settings > Notifications > Canary > Toggle ON Badges.
Android
On Android, you will find this in device Settings > Notifications > Canary > Toggle ON Badges.