In a nutshell, to determine your canonical user ID:
- Sign In to the AWS Management Console
- Open the S3 console
- Select a bucket
- Click on the Permissions link
- Your canonical user ID can be found user the 'Access for your AWS account: Account' heading (e.g., 0123456789abcde0123456789abcde0123456789abcde0123456789abcde0123)
NOTE: a canonical user ID is different from a 12-digit AWS Account ID