It would be a significant overstatement to say that freedom of speech is an illusion in Canada. One can criticize the government with no fear of retaliation and Canada has a vibrant and diverse public sphere, with a wide range of outlets including both social and traditional media. One could, however, support the more modest thesis that although Canada does have freedom of speech, there are a few areas in which this freedom is limited or imperfect.
The first limitation on free speech has to do with national security. The Official Secrets Act limits disclosure of sensitive government information. Although this is important in certain areas of military security, many have argued that this has been used simply to prevent embarrassment of politicians and has limited the freedom of the press and public access to information important to voters in making political decisions.
Next, libel or defamation laws allow people who have been harmed by public speech to sue for damages. Many have argued that Canadian libel laws serve to silence victims in discrimination and sexual assault cases, letting the very rich use the legal system to silence those who might reveal bad behavior. Certain groups are campaigned to reform defamation laws to make it easier for people to speak out without fear of lawsuits.
Finally, laws against hate speech can silence people who might have certain unpopular political views and even limit publication of or accessibility to books expressing unorthodox opinions.