Welcome to FT!

I've done checkin before ORD-YYZ-HKG and ORD-LAX-HKG where I've been given both boarding passes at ORD.

From both routes I've been given op-up at the YYZ or LAX gate even though holding an AA issued BP for the CX flight.

Another trick (well, not really a trick) I like to do is to go to the CX checkin desk and just "re-confirm they have my bags". Doing that automatically causes them to tear up my AA BP and issue me a CX one instead. I figure doing that may increase my chances of op-up but I honestly have no idea if it really does or not.

Also, on some routes your SL status will give you more op-ups than others. For example, on LAX-HKG SL has very poor chance for op-up. For YYZ-HKG sector SL has very good chance for op-up. I don't know what kind of traffic CX will get on the ORD-HKG route, so it really depends on that.

Don't bother asking at ORD gate, if you've been op-up'ed then the computer will tell them when they scan your BP during boarding.