> Even with CanvasBlocker the "check your fingerprint" sites still show a unique fingerprint (but canvasblocker has a ton of really obscure options that I don't understand)

It always be unique, because it's randomly generated. But every visit will have a completely different unique value, which means that the fingerprint from the canvas is a useless value.

The setting in Firefox about:config privacy.resistFingerprinting includes mitigations for some canvas fingerprinting attacks. It's part of a push to bring into Firefox privacy features from the TOR project.

https://wiki.mozilla.org/Security/Fingerprinting

Could there be some way to randomize the canvas and audio fingerprints? An extension that obfuscates them in some sense by sending false signals?

Edit: Perhaps overloading the toDataURL() function to add random noise. https://browserleaks.com/canvas#how-does-it-work

    window.HTMLCanvasElement.prototype.toDataURL = undefined;
    window.CanvasRenderingContext2D.prototype.getImageData = undefined;

kills canvas fingerprinting