Touring bikes come is several styles:
Light touring, for day rides, supported tours, and carrying light luggage (Trek Pilot/Specialized Sequoia)
Medium tourer, handles well without luggage and good for a few weeks of light camping (Trek 520/Fuji).
Expedition tourer: rugged load-carrier for extended self-supported expeditions but can feel sluggish unladen (Bruce Gordon BLT/Thorn EXP)

For a century and general fitness training, the light tourer makes sense. You can use them for commuting and shopping as well. Do note the tyre clearance at the frame, forks and brakes. This should be more generous than on a racer.
The big manufacturers often misunderstand touring and give inappropriate gearing/tyre clearance and riding position. Touring is really a niche market best served by smaller companies.