As David has just made reference to, those specifications correspond to what are known as post-panamax classifications for ships. It's a measurement established by the Panama Canal Authority and it essentially sets the limit for the size of ship that can navigate the canal. No Canadian shipyards claim to be able to lay down a hull in excess of the post-panamax measurements. That's the reason this type of ship would go to zero duty immediately upon entry into force of the agreement, simply because it wouldn't be competing with any Canadian shipbuilder.
On March 10th, 2008. See this statement in context.