Sometimes more than one ending can be canonical too. For example, in Tekken, endings like Panda's, Ganryu's or Lei's have nothing to do with whether they won the tournament or not. Panda's endings are usually about her rejecting Kuma's tokens of love and Ganryu similarly getting rejected by Julia. Lei's ending in T3 was just him doing a martial arts demonstration and in 5, it was him humourously apprehending a random crook.

There can also be instances of compromised endings and half-truths that all add up to a big canonical story. In Tekken 3, Paul's ending is canon because the story dictates that he DID defeat Ogre, but left in an excited fluster without realising that Ogre transformed to True Ogre, which was defeated by Jin.

I think it's always fun to try and guess who's ending is the canon. It is obvious most of time, but sometimes not so. In Tekken 5, Jin's ending was a fairly long one and he was also the main protagonist which usually indicates that it's canon, but the notion of him assuming control of the Zaibatsu and becoming pure evil seemed pretty farfetched at the time. We didn't find out that it was actually true until Tekken 6, which I think is also up for interpretation. I'm torn between Kazuya's ending and Lars' Scenario Campaign ending.

Either way, it looks like Jin has been written off.