Guy we have TONS of official media that gives us a very good picture of what Game Freak considers Canon.
>Gen 1:Origins shows that Red picked Charmander, and Blue picked Squirtle:
https://www.youtube.com/watch?v=UfxmHCtj5cIGenerations re-establishes this:
https://www.youtube.com/watch?v=ktskEn5q7ggNote: Episode 1 of Generations did NOT show Red picking Bulbasaur. It showed "TRAINER", who skips right to catching Pikachu, and then follows the Pikachu in an action montage. It was clearly not representing anything canonical, especially when the following episodes re-establish the starter choices made in Origins to be the canon ones.
>Gen 2:Generations shows that Ethan is the canonical protagonist:
https://www.youtube.com/watch?v=hlh4jKv184ENote: Ethan has, in every form of media, been shown to have Typhlosion, and Silver having a Feraligatr. Lyra has Marill.
>Gen 3:The animated trailer shows that Brendan is the protagonist, and that he started with Treeko:
https://www.youtube.com/watch?v=Vw6zP7n0aisNote: May is shown with both a Torchic and a Mudkip here, but as you know, she'll use the Torchic in the game. This is reinforced by May using Blaziken in counterpart media too.
>Black 2 & White 2:The animated trailer shows Nate as the Protagonist, and that Rosa picked Snivy, meaning Nate picked Tepig:
https://www.youtube.com/watch?v=TFTc3PjjCD4All the other games are more ambiguous, and left up to fan interpretation. Some will say that Hilda/Hilbert chose Tepig, so that Cheren/Bianca would get Oshawott/Snivy to match their color schemes, similar to Gen 1. But none of that is confirmed or official. It's possible that Generations may reveal more about which characters and starter choices are canon, but more likely than not, it will be left mostly ambiguous.
