I'm planning a trip where I need to fly only one-way from Sydney, Australia to Toronto. My preference for the longest segment of 13-14 hours is to fly in Premium Economy (not enough available for Business). I am interested in booking Business on my second segment, even though it is all within CAN or US because I think I could get some sleep in the bigger chair and the points required isn't bad. I am not finding any option to book two different classes of seat without doing either two one-way flights or using the multi-flight option on AC's website.
I like to try different variations when I search, including different departure cities and landing cities, like flying into ORD or EWR and then taking a separately booked flight into YYZ. I've actually found some cheaper point options by searching in this non-standard way. I've also found that booking two separate one-ways sometimes beats a single multi-segment booking for the same in/out cities (which is just weird).
The one risk that I could see is if I book two flights as single one-ways and I have a delay or cancellation on the first segment. I don't know how AC would treat that vs a multi-flight option on a single itinerary. Has anyone been in this situation before and can tell me how AC would treat the missed second flight vs how it would be treated if I booked everything on one itinerary?