This question already has an answer here:
For dual citizens I know which passport to show at which step when travelling between the two.
But now I'm adding a new complication.
Let's say I have citizenship in the Us and Canada and (born in US, live in Canada).
Travelling from Canada to Japan with a layover in the US. Who sees what passport? When I enter the US they'll want to see my US passport but what do I show to enter Japan? I'm assuming the Canadian passport since its where I actually live (and what matches the passport of my travelling companion).
And what about the return trip?
(edited for specific countries)