Yes, it's true. These characters are gay in canon. (I consider gay in canon stories to be slash, mostly because the term is more useful if it covers all gay fan fiction, as opposed to just gay-against-canon fan fiction.)
Best FF That the Canon Author Would Probably Really Have Liked, Assuming He or She Even Existed:
Follower, by the oft-nominated Gloria Mundi. The Illiad, Achilles/Patroclus. Troy, when it comes out, may attempt to convince us that Achilles and Patroclus were just good friends, but I, for one, will keep the faith and remember these guys as Homer made them: pure slashy goodness. (Well, in Patroclus' case. Achilles was more like pure slashy whininess.) This story is a short, sad reflection on Achilles' relationship to Patroclus, with both guys very much in character.
Best FF Involving Superheroes as We All Know They're Meant to Be: Gay, in Love, and in Spandex:
The Business, by Basingstoke. The Authority, Apollo/Midnighter. All Midnighter wants is one number, but it's the one number none of us can ever have. You don't need to read the comic books to understand this one perfectly. But you probably should read them anyway. It's got gay superheroes. Spandex! Masks! And in-canon groping! What's not to love?
Best FF Featuring a Ewan McGregor Character as the Sane One:
Curious, by Jane St. Clair. Velvet Goldmine, Arthur Stuart/Curt Wild. At the end of the movie, we get a glimpse of a much-changed Curt Wild. This story explains the change. Explains a lot about Arthur, too. And, as I said, Curt's the sane one in this. You know an author kicks ass when she can make you believe in the basic mental stability of a character played by McGregor, the God of Neuroses.
Best FF That Explains Why Sometimes It's Best to Skip the Forgiving and Just Forget:
As I Went down in the River to Pray, by Halrloprillalar. Greek mythology, and to tell the pairing would spoil the story. Hal changes a bit from the traditional version of this story, but it works even better than the original. And, look, I can't tell you much about this one, obviously, but if you're a myth geek, you'll figure out what this is based on in a few paragraphs and squeal with joy. And if you've never read Greek myths, you'll love it anyway for the unusual, wonderful ending. (Although let me say unto you: read Greek myths. They are the holy grail of canon slashiness.)