Thank you. So, it seems that when a US/Can citizen flies from US to Can, authorities in both countries are indifferent between the following:
1. Check in with the airline using the US passport, enter Canada using US passport
2. Check in with the airline using the US passport, enter Canada using CA passport
3. Check in with the airline using the CA passport, enter Canada using CA passport
Is this correct?
Still, options 2 or 3 seem to make the most sense to me, with option 2 being the best.
You're overthinking it. If OLCI, just use the passport that let you OLCI (eg the passport that does not require a visa). At the airport/gate show agent both passports and let the airline sort it out.
There is no clear definition as to what "without a valid US passport" or what "to bear" a US passport actually mean
Does it mean passenger merely need to have a passport issued covering travel period but not physically with them?
Does it mean passenger need to have passport physically in their possession?
Does it mean it has to be reflected in APIS submission by airline? There's is nothing to say APIS contains foreign passport and passenger presenting US passport at primary inspection is against regulation.
There is no enforcement penalty defined on this regulation either.