Canon has released a statement in which it apologizes for the postponement of recently announced lenses. The EF 8-15mm f/4L, EF 300mm f/2.8L IS II, and EF 400mm f/2.8L IS II were all scheduled to be released in March 2011.
However, the recent earthquake in Japan caused damage to its manufacturing plants and, as a result, the availability of these lenses is currently unknown. Canon stated that it will provide an update on the availability of these lenses once that date becomes clear. Note that B&H Photo has listed an approximate availability date of May for the 8-15mm and 400mm lenses (see above links).