A particular piece of fanfiction can conform to canon, or not, at the discretion of the author.
Different fandoms have developed terminologies unique to their canonical material and will have a Fanfiction Glossary specific to their source, whether written or unwritten.
This is the very definition of a Mary Sue in male form (see A Fanfiction Glossary) and Wesley was widely believed to be Gene Roddenberry's 'Mary Sue', the character that most represented what Gene would want to be on a starship.
Fanfiction.net has a special category for Twilight FanFiction with more than 2,000 pages of choices.
Fanfiction also hosts a Best of Twilight Community where the best of the Twilight collection of fan fiction is listed.