>>1
Canon is basically ideas/facts/etc from the 'official' story. Basically, "Canon story" is the official story you read or watch in the manga/anime; "Canon Pairings" is pairings (couples) that are hinted or that really happen on the official story.
For example, on the canon story of naruto there is the canon pairing of Naruto and Hinata (even if Naruto is dumb as fuck and doesn't notice it... *cough*)...
...that or im going with
>>2.