A knife is lethal force. That means, that without question, you can use lethal force to defend yourself.
If you don't think so, point out in where in
relevant section of the Criminal Code of Canada that supports that fact. I have reviewed it briefly, and I cannot find anything regarding this situation, where it would invalidate a self defense justification.
Understand that if somehow it makes it to trial, you will be defending yourself in front of a jury, not a single judge.