McCarthyism targeted people for possibly (and often not actually) supporting a legal political movement. Supporting terrorist organizations and that being made public isn't the same thing. And an individual or group using a website announcing someone's public actions isn't the same thing. McCarthy abused his authority as a member of the federal government to harass and and punish. Canary mission has no such authority. It just turns out a lot of people don't like people who side with terrorists.
That being said, I am not really a fan of canary mission. I think more work needs to be done on education and understanding of the entire situation instead of a few of the most recent events. If I were still in the US, I would probably try to organize such groups. But it is definitely a much harder goal to accomplish.