Just because they say it, it doesn't mean it's true. And just because the Sun isn't part of the OPC, it doesn't mean they print blatant lies. Have there been any stories that The Sun has reported on where they took an opposing (and falsifiable) stance to other newspapers? Have they invented any stories out of thin air to drag anyone's name through the mud? The laws on libel are pretty strict in Canada, and no media organization is going to go out and just make shit up - no matter their political leanings, they're aren't going to open themselves up to constant litigation by printing false information under the guise of news. Tabloids get away with a lot because they clearly state inside the paper that it's "for entertainment purposes only".
Don't get me wrong - I dislike the Sun as much as a lot of people here do. And I don't necessarily agree with the editorial angle they sometimes take. But that doesn't make them blatant, fact-altering liars.
For what it's worth, the OPC itself states that it doesn't go anywhere near anything that's an Opinion - so Rosie Dimanno or Christopher Hume or Margaret Wente or Royson James can espouse an "opinion" that flies in the face of common sense or fact, and the OPC won't touch it with a ten foot pole. So even if The Sun was part of the OPC, they still wouldn't go near Sue Ann Levy.