Admissibility would come down to if he has said or done anything illegal or just something a bunch of us consider shitty. Shitty people come to Canada all the time, from all over the political/ideological spectrum. We don’t exclude people from the country or kick them out based just on ideas they express unless they transgress our laws.
I don’t know this case or the person or what they’ve said. I’d be surprised if it could be demonstrated that they advocate genocide as defined by our laws, and they still get let in. That would be a serious miss.
What happens quite a bit is people will be on one side or another of some conflict, are outspoken and say things that piss a lot of people off, and then they come to Canada to speak. Public pressure campaigns will be mounted to encourage the government not to let them in or to kick them out, but it ultimately hinges on what evidence is actually available to the administrative decision maker, and how that evidence matters under our laws.
That’s just my description of what the system is. Personally I’d be fine with Canada’s borders being a bit less open to non-citizens and non-residents who are just coming here to stir up shit, but that would also apply agnostically to anyone coming here not in good faith, I don’t care if someone’s far left, far right, white, brown, black, or what exactly they’re advocating for. My personal belief is Canada could use fewer strangers coming here to stir up shit for their cause back home. I rationalize this based on the principle of our country having absolute sovereignty over who comes in, and nobody without legal status has an entitlement to expect to get to enter Canada.