100% unique mean that is not really natural, canvas should not be unique but changed in order to be natural.
Unique canvas fingerprints will do much worse.
Is like you said you have a device that never exist.
To better understand how this work :
Google already have a full database with all kind of canvas signatures from all worldwide devices (iphone, android, computers, etc...), and if your canvas signature will not match on them database then you fail, it is a prove that your canvas is fake. If you try to spoof the signature then image pixel parameters will not match and again you fail so is almoust imposible to pass canvas.
On default settings may make it pass the google test.
For example google will not ask for SMS confirmation when a new gmail account is created because he trust the device you use.
Most of people must understand why unique signatures is bad practice and all softwares that spoof parameters will make traking services to detect the device much easy