It wouldn't take much more of the progressive agenda here in the US to see the same thing happen here. We're treading on slippery ground.
That area is, in fact, one area where I make common cause with those who see nothing but bad in Islam - there has been constant pressure to "liberalize" (pun intended) the defamation laws in this country so that defamation of Islam, or its mangy cur of a prophet (I'm going to say it while I still can, not because I necessarily believe it), is actionable and the defamer subject to damages. To date that pressure has been resisted - unlike much of the rest of the world, the US pretty much shut down defamation as a serious tort many decades ago. Public figures almost never win a defamation suit - and that includes individuals who interject themselves into public debates, and "public" doesn't have to be the entire public at large, but can include a large body of individuals who have a common interest, such as a large national association. Mr. Warman would have almost certainly be treated as a public figure and would therefore have had to show that these two people acted with the intent to cause harm, or with reckless disregard for the truth; in other words, Warman would have lost.
And he would have lost big because when someone sues for defamation (at least in the US) almost their entire life becomes relevant to the issues and a well-represented defendant can usually use the suit as a means of airing almost all of the plaintiff's dirty laundry.
Honestly, these two should expatriate from Canada, drop their Canadian citizenship and take up citizenship elsewhere, someplace where their freedom to speak will be respected; they can then, if they wish, continue to run an open forum about Canadian politics with little risk of further liability, and certainly without risk of prison. I would have suggested they move to the US, and 5 years ago that would have been good advice; now, I'd advise them to wait until after the 2016 elections, or at the very least until after the 2014 elections.