I honestly don't think it matters ... let your shifters be your guide -- in other words, probably cantilevers ...
FWIW. Regardless, for loaded touring in the Rockies, I think you want one of those Shimano hubs which has a DRUM brake which you will use as a THIRD, drag brake to scrub speed off during descents.
A rear disc brake would be another option for a drag brake if your frame has disc brake mounts.
A v-brake is a cantilever, it is a direct pull cantilever to be exact. You will find that a direct pull canti will have the most stopping power. Search sheldon browns site for real good info.