If we took our Britax Boulevard and it fit, I am pretty sure anything would fit! You can always call the airline and check if there are any restrictions on the width or height of the car seat but I think most of them are fine these days.
That being said, I have had fantastic luck giving my kids Benadryl just before we board the plane. My pediatrician suggested it because sometimes little ones have trouble with their ears on planes. If you go this route, be sure to try Benadryl on your child BEFORE your trip. Some children get super hyper on it, although most children (thank goodness mine included) fall asleep. Honestly the best thing you can hope for with a baby/toddler is that they will sleep through most of the trip.
If the Benadryl thing won't work for you, then bring a portable DVD player (or laptop) if watching TV interests your baby. We have used Baby Einstein DVDs with success on planes. I brought little headphones so they could listen. If you buy a new DVD, that works best since it's always more interesting when it's new. A magna doodle will usually work for a few minutes too.
Other than that, bring more snacks and diapers than you think you could ever possibly use (this came in super handy when our connecting flight to Hawaii was delayed for 14 hours and I had a newborn and a 2 year old...).
Bon voyage!