While Holocaust denial is loathsome, it shouldn't be a criminal act.
Why not?
It seemed to work just fine for us. (Although the Supreme court did eventually rule that it wasn't a criminal act)
You'll have to persuade us why it should be illegal. For speech to be a criminal act, that would have to be some extraordinary persuasion.
Are you familiar with Ernst Zundel? He is the guy who published that pamphlet here in Canada and was convicted for it. Eventually it was overturned by the supreme court but he was initially convicted for incitement of hatred thru the spreading of false news and that conviction survived an initial appeal.
Canada has never been a nation of absolutes; we will curb behavior that is determined to be detrimental to the stability of the country. Hell, we even have a 'fuck what the constitution and the court says' clause written in the constitution. In responsible hands it has served us reasonably well. But it is a very different mindset than the U.S.