The U.S. and Canada missed a Friday deadline imposed by the Trump administration to revamp the North American Free Trade Agreement, but agreed to extend talks rather than rip up the quarter-century-old treaty.

After four days of marathon talks ended with significant differences remaining, President Trump said he still planned to stick with the timetable he laid out earlier this week to sign a new pact in late November to replace the three-nation accord he has branded “a disaster.”

But...