On Sunday morning, the China Ocean Shipping Co. containership Andronikos will transit the Agua Clara Locks on the Atlantic Ocean side of the Panama Canal. In the afternoon, the Andronikos will sail through the Cocoli Locks facing the Pacific Ocean. As the sun sets over Panama, the vessel, which holds up to 9,400 twenty-foot equivalent unit (TEU) boxes, will have been the first to make its way through the expanded canal.

Nearly 10 years in the building and nearly two years behind schedule, the canal will open June 26 with two new sets of locks—one each on the Atlantic and Pacific sides—creating a new lane of traffic, and with existing channels that have been widened and deepened. The regularly scheduled sailings begin Monday, with 100 giant "neo-Panamax" ships capable of handling up to 13,000 TEUs already holding reservations to sail through a waterway that will accommodate two and a half times the vessel capacity it could 10 years ago.

The inauguration of the $5.4 billion project will put to rest the decade-long speculation on the impact of the expanded canal on trade flow between Asia and the eastern half of the U.S., where most of the goods-consuming population resides. The betting has centered on whether cargo arriving from Asia would be directed on an all-water routing through the canal, or call at West Coast ports and then be trans-loaded for an inland move by rail or truck, a more expensive, but faster, proposition.

David Egan, head of industrial and logistics research in the Americas for Los Angeles-based real estate services giant CBRE Group Inc., said the canal's opening is unlikely to meaningfully move the needle on West Coast freight volumes. Most of the freight diversion from the West Coast to the East has already taken place, Egan said. In the late 1990s and early 2000s, about 60 percent of U.S. imports transited through the West Coast. Egan reckons the figure today is closer to 52 percent, as several labor-management disputes along the West Coast over the past 14 years convinced shippers and retailers to diversify their arrival nodes to avoid service disruptions.

At most, the canal may divert a couple of percentage points of market share to the East, bringing the coasts effectively into equilibrium. Most U.S consignees have their supply chains calibrated they way they want them, he added.

A potential game-changer would be if sources of production shifted from China and other Asian manufacturing locations to India and other markets that wouldn't rely on the Pacific as a means of waterborne transportation, Egan said. Such a shift, if it occurs, is decades away, he added.

Walter Kemmsies, managing director for the U.S. Ports, Airports, and Global Infrastructure Group at Chicago-based real estate and logistics giant JLL, takes a different view. Shippers and consignees may be surprised to find the canal is competitively priced to handle the mega-vessels that will dominate the seas in the years ahead, according to Kemmsies. In addition, the Panama Canal Authority, which operates the canal, is offering what Kemmsies called "frequent flyer"-type volume discounts on fees charged to use the new locks.

Any cargo shifts to the East Coast will depend on whether the railroads lower their rates on inland moves off the West Coast, something the rails have been loath to do. Consultancy Drewry Supply Chain Advisors had calculated that, as recently as March, rates on the rail portion of an eastbound intermodal move from Los Angeles to Chicago had declined at a much slower pace than the port-to-port component from Shanghai to Los Angeles, where spot rates had virtually collapsed.

Kemmsies said in an e-mail that the railroads, as publicly traded, private-sector companies, have a "natural conflict of objectives" with West Coast ports. "Port authorities want a lot of volume. Railroads want a lot of revenue," he said. "Railroads are profit maximizers."

Egan added that railroads passed on an opportunity to lower inland rates during, and in the aftermath of, the West Coast port slowdown in late 2014 and early 2015 to help businesses already hurting financially from delays and shipment backlogs. "If they were going to do it, that was the time," he said.

Kemmsies and Egan said the expanded canal would take market share from the Suez Canal, which has historically handled mega-ships sailing from East Asia to the U.S. East Coast. However, Egan said the Suez has not ignored the new competitive threat. It has, and will continue to, lower tolling rates in order to defend market share, he said.