Next week I'm going on my first multi-partner itinerary using United miles, and I'm realizing that it's possible carry-on rules aren't going to be the same as I'm used to domestically. I'm flying Asiana J (QS seats expected) across the ocean, Singapore and ANA regional J in Asia, and then ANA First Square home. Will my roller bag, which generally fits (with minor shoving, when full as I expect it to be) in the overhead of 737-type planes but not the small overheads of the regional jets, be okay both in terms of size, and legality? I really want to avoid accidentally having to check it. I'll also be carrying a backpack, but nothing else.