If you have a photo taken with that specific camera, you can often find the serial number in the EXIF metadata.
Every photo you take contains hidden metadata called EXIF, which includes your camera's unique serial number (as long as a software bug isn't affecting it). If you have (JPEG or RAW) taken with your camera, you can extract the serial number. how to check canon camera serial number best
This is the official Canon tethering software. If you have a photo taken with that
This is the most common physical feature. how to check canon camera serial number best