I have floated this question over at the BA forum, but I will ask here as well.

I have a trip coming up where BA handle the flights to/from USA, but there are a couple of AA domestic legs (two connectng flights to enable me to get where I need to be - SJC-DFW-YYZ). Given all the current problems at airports both in the UK and the USA, I am considering doing the whole trip with a large carry-on plus a small backpack.

My carry-on bag is the largest 'legal' size for BA, however at 56 x 45 x 25cm (22 x 18 x 10in) it is larger than AA's allowance. Straight up, what is the likelihood of being told I must check it in or is there some flexibility in AA's policy when it comes to international pax? As a side point, the domestic leg is not immediately on arrival or departure from the US. It is in the middle of a two week trip.

Also, both legs are a 737 and I am flying in MCE if that makes a difference?