The other possible biometric that has been proven to be reliable is retina scans. Of course, they're already being used in, for example, CBSA's NEXUS program, which speeds up or facilitates the crossing of the border. I'm not aware of whether retina scans were ever considered by CIC in setting up their biometrics program, or, if so, for what reason they might have been rejected.
On February 16th, 2012. See this statement in context.