Since his son is still growing, I would probably be inclined to go up a size from where he is today. They should be able to make adjustments to make it fit him now and re-adjust later as he grows.
For a long trip like that, I might consider investing in a decent set of wheels with deeper rims. Something like 40mm rims gives you more roll. I don't think I would go much more than that as it can make riding in wind a real challenge.
Personally, I like Specialized and Felt. My road bike is a Specialized Roubaix with lower-end components. My tri-bike is a Felt B12 (nicely loaded). Trek also makes really nice bikes. As I said earlier, fit and comfort are the most important aspects.
I will make a plug for choosing a high quality saddle. For long rides, having a comfortable saddle is crucial. When I got my Tri-Bike, I bought an ISM Adamo saddle. It is amazing. I liked it so much, I bought an ISM racing saddle for my road bike. They aren't cheap (~$250), but for long rides they make a HUGE difference. I would encourage your friend's son to try out a bunch of different saddles on the bike he chooses and buy one that feels best to him. A good bike shop should have demo models for you to test drive for a weekend or longer.