Triple is definitely the way to go for loaded touring if you are planning on any significant climbs.

I have two touring bikes, both with triples. I live out West so no mountains is usually not an option.

For light touring I have a Gunnar Sport with a Sugino XD-600? 46-36-24 crank and a Campy 13-29 cassette with Chorus front and rear derailleurs. I use Centuar brifters and it works fine.

For heavier touring I have a Long Haul Trucker with an XT triple 44-34-22 and 11-34 casette. XT rear derailleur and Tiagra front derailleur. I have the Dura-Ace bar end shifters on that one and they're great. Campy triples, IMO, shift and especially trim better than Shimano, but I agree that you should have no problem with a decent-level Shimano triple. And, of course, the bar end shifters make shifting perfect on a triple, since you can manually trim the front end easily. By the way, the Sugino XD triples are definitely available and give you a much lower option than standard Shimano or Campy triple road cranks.

The simplest and most easily available way to go would probably be with XT RD and 11-34 cassette, Tiagra triple FD, XT 44-34-22 crank and Dura-Ace bar ends. There are differences of opinion on these pages between bar ends and brifters. But I will tell you I have both and like both. They're just different, but you get used to both. The buttery smoothness of the trim on the bar end front shifter is really nice with a triple. Some people say they favor brifters for their quick and easy shifting, but remember that your shifting pattern is a lot different when you are touring than on a quick fast training ride on a road bike.

From your comments I think it is unlikely that your LBS guy has ever done any touring. You will really be glad you have the lower gearing and the smaller steps of a triple at the end of a long day, facing that last long hill or mountain. This is especially true for you since you say you plan to use the bike primarily for mountain tours. I would listen more to the people on this page, especially the ones who have done some longer tours in mountains.