Main purpose of the NW Heartland Corridor project is to open up clearance for shipping containers inland that arrive via Panama Canal on the bigger ships. Several other E.Coast ports are also working on expansions with rail connections inland. The stuff that comes off the boat at LA etc directly to the train to Chicago and points east is vulnerable. Costs much less for most cargo to stay on the ship unless there's value added (like consolidation and re-shipping near a W.Coast port) or there's a real need for travel time of a day or 2 less.

Of course, Lazaro Cardenas (MX) was supposed to eat LA's lunch because of shorter runs to the Midwest but so far hasn't. According to an interview I read much of the Lazaro Cardenas traffic is internal to MX. So as with most other things in the shipping business we'll just have to wait and see. I would, however, expect lower-value traffic going to the E.Coast and Midwest to stay on the ship through the Canal which might hit LA and other West Coast ports a bit.

Another thought: the LA Metro economy alone is bigger than some states' even with a down economy. I don't know how much LA port traffic has local (within a few 100 miles) final destinations, but it's probably a lot. So even if the cross-country traffic takes a hit from the bigger Canal the ports in LA at least should stay fairly busy.