Sorry to dig up an old thread...I'm looking at booking a multicity with AC with the same idea: YYZ - SFO, SFO - EWR, EWR - YYZ.
I'm guessing the correct answer is there's no way to earn SQD on the SFO-EWR leg, as the only *A operating that route is UA.
However, the error message at the top of the page got me curious:
It is not possible to book a flight segment between
two cities in the same country, unless that country is Canada.
Please contact
Air Canada Reservations for assistance with this type of booking.
Is there a way to get AC Reservations (by phone) to actually issue an itinerary like this? Even if they did, would the ticket number (stock) be 014 (AC), or 016 (UA) for SFO-EWR?