You can accomplish what your are looking for with AutoPebble and Tasker. AutoPebble allows Tasker to react to button presses on your Pebble watch. Tasker can then launch a different Pebble app (AutoPebble plugin action) or load a different Canvas watch face. I use this to cycle between 2 different Canvas watch faces with the bottom button and to load different apps with the top button (freeCaddie, Roku remote, or NavMe depending on other variables set in Tasker). I also use the middle button to launch PebbleTasker with a menu tree to get to several other Tasker tasks.