I built my wheels for my custom touring bike last year. 26" MTB rims on road hubs. 36 spoke rear, 32 spoke front. Mavic X618 rims, Ultegra hubs, butted 14-15-14 spokes, 9 speed cassette. I run 26x1.3 tires on the road, 26x1.5 off road.

By going custom, you can pick rims of the width for the tires you'll use touring, and for the weight you'll carry. You won't want wheels built for MTBs, and pre-built touring wheels may not exist. You definitely don't want low-spoke count wheels or bladed spokes or proprietary spoke/hub designs.