I am booked late Jan YYZ-ORD-SFO. I can preselect seats on the AC flight outbound, but cannot select seats on the AC website or the UA website for the UA flight. Its a codeshare. UA gave me my UA PNR but UA.com says I cannot book seats for the flight, nor will it display a seatmap. So how do I get an assigned seat for the ORD leg. There are a lot of crappy seats on the 319. Also is it possible to get the option to pay for ex+. If I cannot be assured of an aisle on the ORD leg, I still have 20 hours or so to cancel the whole thing without penalty, and fly someone else. I am booked in T+.