Some years ago I took a cruise to Alaska. Now the logical place to begin an Alaskan cruise is Seattle. However, the cruise ship was a Dutch liner. Because of the Jones Act, the line can't take passengers from Settle to Alaska. So it leaves from Vancouver, just across the Canadian border. All the shore activities associated with the cruise, such as refueling and re-supplying the ship, take place in Vancouver. If tourists arrive early, they spend money in Vancouver. In short, a lot of money that would logically be spent in Seattle is instead spent in Vancouver. All in the name of preserving jobs
aboard ship for American sailors.
The Jones Act doesn't preserve American maritime jobs, or American shipbuilding jobs. Instead it enriches Canadians.
I may be wrong about this, but I think the only impact the Jones Act has on the trip you described is that a foreign-flagged vessel that travels between Seattle and Alaska must first make a stop in Vancouver so that it's considered an international voyage rather than a domestic one.
Maybe that cruise line was simply running ships directly from Vancouver to Alaska because it had better berthing arrangements in Vancouver?