Sorry, not been upgraded on the cruise. Your flight time is not bad really considering some times you can be left at the airport until a flight at 7pm. By the time you get off the ship as you will probably be one of the last off and then drive to the airport, do the whole luggage thing, checkin, go through passport control etc it only leaves a little time for a snack and some shopping. So yes you will be left at the airport for hours but then you need to be especially in the US.
If you have been many times with Cunard you will stand a chance of upgrading if the cabins above are well underbooked. If you have to spend some time at the airport and there are just two of you it is always worth considering booking a place in one of the private or "executive" lounges, the cost is normally about $20/40 each and for that you have drinks, and snacks, comfortable lounge chairs, and peace and quiet to spend up to three hours in before your flight. These are particularly good if you are a nervous flier. Just Google "Airport Lounges" for the various options ......Id.