Completion of the massive, multibillion-dollar project had originally been set for October 2014 but has been successively pushed back because of construction and labor problems, legal issues and the discovery last year of fissures in one of the widened locks.
Authorities had said most recently that they were looking to May or June to declare the work on the century-old canal finished.
"In around 10 days at most we should be well-placed to effectively say that we will be able to let through commercial traffic at the end of June," the Canal Authority's CEO, Jorge Quijano, said.
"At this stage I don't see why that wouldn't happen."
Quijano said the Spanish-led GUPC consortium leading the expansion work is in a "most critical" phase of testing the reinforced canal. If those tests are deemed successful in around 10 days, the end-June date for the inauguration could be confirmed.
Panamanian President Juan Carlos Varela is to visit the work in progress next week and may declare the exact date, Quijano said.
Work to enlarge the 50-mile long waterway so that it can handle more traffic and bigger cargo ships started in 2007.
The cost of the project has ballooned from an initially budgeted $5.3 billion to around $7 billion.
Around five percent of the world's commercial shipping passes through the Panama Canal.
The Central American country earns $1 billion a year in revenue from shipping fees for using the canal. With the expansion, it hopes to triple that within a decade.