I suspect you'll find that because of the number of boxes on the ship, if the Canal is expanded to allow the really big ones it'll be cheaper for non-time-sensitive freight to go as far by ship as possible. There are some ships in service now that are so big only one port currently in use on the West Coast can handle them: Long Beach, though the Mexicans are working on fixing that. Lazaro Cardenas (MX) is interesting because it has a rail connection to the Midwest (KCS system) that's shorter than than the trip from LA/LB. Prince Rupert (BC) is in play too, but is a bit farther from the major Midwest markets than the others so it has to work other angles (like better reliability due to less congestion, etc.).

For comparing time, the ship should be compared to ordinary stack trains - that get only slightly higher priority than loose-car freight. Obviously, if you drop the boxes on a Z-train (40-45 hours to CHI) it'll get to the Midwest from LA much faster than any ship can do it. There is some time-sensitive sea-intermodal freight - stuff that's heavier or higher-cube than will easily fit a plane, or that's sensitive in the sense of being on a schedule and trackable, but doesn't have to get there overnight. Car parts for instance. For ordinary cargo on an ordinary stack train, shooting the ship through the Canal and straight to Houston might be time-competitive to grounding at a West Coast port and using RR from there, but bigger ships are needed to make the numbers dance. Fastest of course is to truck it direct to the customer from the port, but you pay for the speed and reliability. Oh yes - another option (which I think TRAINS did an article on) might be to ship to Panama, rail across, and ship beyond - not as crazy as it sounds now that the Panama Rwy has been rebuilt by a KCS affiliate.