Open your HTML email signature file in your web browser.
Press Ctrl + A to select the entire email signature, then press Ctrl + C to copy it.
IMPORTANT: Do not use your mouse to select the area, only use Ctrl + A as you may miss out on grabbing some of the code.
Open Canary Mail for Windows, then select Preferences from the left menu.
From the Preferences window select Signatures on the left side, then select Signature 1 from the Signatures list.
Click inside the signature text field and highlight the Sent from Canary text, then hit delete. Hit Ctrl + V to paste your copied email signature. Hit Save.
Close out of your preferences and compose a new email. Your email signature will now be automatically inserted when writing new emails from Canary Mail for Windows.