Very few people realize the power of css positioning. To set the map to occupy 100% height of it's parent container do following:
#map_canvas_container {position: relative;}
#map_canvas {position: absolute; top: 0; right: 0; bottom: 0; left: 0;}
If you have any non absolutely positioned elements inside #map_canvas_container they will set the height of it and the map will take the exact available space.