It sounds like a false positive, unless you're showing ads in the Manager.
Some parts of the Manager use canvas tags, but I'd be really surprised if there's any canvas fingerprinting going on.
I wasn't aware that the Manager uses canvas tags. But that clearly explains the possibility of a false positive, the Canvas Defender web extension can be quite sensitive at times. Thanks for responding Bob!
I wasn't aware of that either, until I searched the core code. I think they may have been introduced when the Manager was altered to be more responsive.