If you're flying the new 2018 J (probably not since you're going tpac back to the US) you may have a problem with it fitting under the seat or in the overhead compartment, as both have shrunk in my (admittedly unscientific) opinion, but I agree with everyone else that SQ doesn't really care what you carry on in J. Or in Y for that matter, I've seen some really crazy things being stuffed into overhead compartments back there.