At common law, defamation covers any communication that tends to lower the esteem of the subject in the minds of ordinary members of the public.

The perspective measuring the esteem is highly contextual, and depends on the view of the potential audience of the communication and their degree of background knowledge. Probably true statements are not excluded, nor are political opinions unless explicitly stated as such.

Intent is always presumed, and it is not necessary to prove that the defendant intended to defame. Where a communication is expressing a fact, it can still be found defamatory through innuendo suggested by the juxtaposition of the text or picture next to other pictures and words.

Broadly, Canadians can be held liable by English-Canadian courts for comments on public affairs, about public figures, which are factually true, and which are broadly believed. They cannot be held liable for opinion, inference, hyperlinking without explicit agreement with the content, reportage when this is based on honest research and journalistic ethics.

Plaintiffs need not prove falsity, malice or damages. Politicians can, and do, sue including during elections for political advantage or to silence critics or accusers. Evidence can be gathered by spies representing themselves falsely in private conversations.

Defendants, once accused, are prima facie liable until they prove themselves innocent (reverse onus). Anonymous persons can be exposed for political comment, even if they are vulnerable and reside in jurisdictions where retribution is likely. People may be sued from remote jurisdictions if publication can be proven in that remote jurisdiction, which can mean as few as one person seeing the words.

source: Wikipedia

(one reason all comments on ODN – have a name attached – or no pseudonyms)