In my experience, VMs with the same or related OS have the same canvas fingerprint. So Firefox in all Debian, Ubuntu etc VMs have the same fingerprint. Tor browser blocks fingerprinting, but Iceweasel doesn't. But if some bug allowed canvas fingerprinting in Whonix Tor browser, it would be the same as Firefox in another Debian-related VM.
Fedora, PCBSD, OSX and Windows VMs on the same host have different canvas fingerprints. Debian-related VMs on different hosts also have different canvas fingerprints.
I haven't experimented with using different graphics drivers in Debian-related VMs. Or with host GPU pass-through