Hi, thanks for all your replies. Here is some more info about my trip:

I will be flying YVR-HKG in a party of three on "Class A" economy next month. Two of my luggage bags are fine (within size), while the third is the oversized one (as quoted in the OP; 3 inches oversize). All three pieces of my luggage are also within the weight limit of 23kg. The problem arises in that I don't own another luggage bag that is within size.

So from the responses above, I'd assume that it'd probably be wiser for me to purchase another bag rather than risking the 3 inches? Or would there be any other solution as I don't really want to go purchase another bag just for this one trip. Thanks again for everyone's help.