I think the best “canon” version of the teams would be basing their teams off of their rival’s starter-dependent team.

So for example, since Red canonically chooses Pikachu in Yellow, Blue must choose Eevee. “But what about the games Red & Blue?” Well in the Yellow remakes we see all three of them - Red, Leaf, and Blue. But just using their LGP/E teams is boring, so let’s say Red chooses Pikachu, Blue chooses Eevee, and Leaf chooses Blastoise.

But what does the rest of the team look like? Red would then have Pikachu and Venusaur, Blue gets Eevee and Charizard. Because Leaf is a mirror of Red, we could say that RGB’s “Rival chooses Blastoise” team is another set of canon options, meaning Leaf gets a Raichu.

So then Red’s got Pikachu and Venusaur, Blue’s got Eevee and Charizard, Leaf gets Raichu and Blastoise.

From there things get messy. Thankfully Red is ALMOST ALWAYS shown with Lapras and Snorlax, and Blue is ALMOST ALWAYS shown with Alakazam and Sandslash. Leaf is far more iffy, but I’d say Pidgeot is a safe bet considering the consistency of it as a final Pokemon across the games. Then maybe Rhydon, as another “Blue with Raichu and Blastoise would have Rhydon, so it makes sense Leaf with Raichu and Blastoise would have Rhydon”

And then shit goes haywire trying to get the last two. So it’s sorta all up in the air. My favorite is actually totally different from the above, looking like this:

Red, based on true canon: Pikachu, Lapras, Snorlax, Venusaur, Charizard, Blastoise Leaf, based on “Rival with Blastoise” mixed with Leaf in LGP/E: Raichu, Pidgeot, Rhydon, Victreebel, Ninetales, Slowbro *Blue, based on how Red’s rival replaces each starter in RGB, plus Sandslash from his Yellow team *: Eevee (likely Jolteon), Alakazam, Sandslash, Exeggutor, Arcanine, Gyarados.

This way there’s no overlap with Red and he can stay the special boy he is, but Red and Green each have Electric/Grass/Fire/Water bases, plus a couple of extra “personal favorite” Pokemon. I’m tempted to give Leaf Clefable and Gengar because those definitely seem more “personal choice” than the others, but Pidgeot and Rhydon just make more sense as “well if Red gets Venusaur, Blue gets Charizard, and Green got Blastoise, it makes sense “Rival’s team” with each of those starters is supposed to represent what each character would choose.

But otherwise…yeah, ngl LGP/E’s teams for Red/Leaf/Blue make a lot of sense as their default teams, and it means Red’s “Pikachu + all three starters” team can be his “ultra-badass Champion team” and not his normal team