You must use the Manual encryption mode (PGP) in Canary if:
1) You plan on using your existing PGP keys generated via other apps / tools such as GPGTools, Symantec Encryption Desktop etc
2) You prefer to manage your encryption manually, using your existing PGP keys instead of SecureSend.
On an Android Device, you can select Manual Encryption Mode via Canary Mail > Settings > Security > Encryption Mode > PGP.
3. Now, click on Import > Browse and select the keys you want to add to the Key Manager.
4. You can also create keys in Canary via Import > Generate Key.