Mine have often gone cargo as puppies because many airlines refuse to let you have the dog in the cabin while the plane is flying over water (the Atlantic Ocean for example). This is why, if the destination was USA, we always flew them to Newark, New Jersey as that was the nearest airport once the Great Ditch had been left astern. Then the owner (I always insisted the owner come and fetch the puppy and fly back in the same plane) could dig the Basenji out of the hold and have it in the cabin for the onward, trans-USA, stretch.
Properly conditioned ahead of the flight, those 5 hours in the hold were a never a problem to the puppy.
I hate those enclosed varikennels airlines insist on but we'd get one in weeks before departure, feed the Basenji in it, give him / her a favourite bone ONLY when inside the kennel and so on.
For the flight, one-way=only diapers formed the bedding so the puppy remained dry even if. . . and I put ice in the drinking bowl so it melted slowly and was less likely to spill than water. Some airport staff seem to think swinging the crate is necessary !
A low residue diet for 48 hours or so before the flight meant the Basenji was less likely to have to soil the bedding. And most airlines have been very good at finding me a grassy space for the puppy just before he/she was embarked. KLM were super - way out the best !
The criteria as to the size of the kennel or the sherpa if pet-in-cabin was sanctioned before travel always seemed to be 'can the dog stand up with comfort' - but sometimes there was a requirement that the animal could also lie down stretched out.
With puppies, these exigencies were no problem but you may find your boy is over the weight limit.
Hope some of this helps - but good luck anyway. If hold travel is the only way, pick a night flight or make sure he has had a good long free run beforehand and is well tired out !