Sadler turned a lap at 153.734 mph around the one-mile, concrete-surfaced Dover track for his fourth pole of the season and the 10th of his Nationwide career.
His lap time was only 0.001 seconds faster than Edwards, who won the Nationwide race here in May.
Stenhouse holds a 14-point advantage over Sadler.
Marc Davis and Tony Raines failed to qualify.
Saturday's 200-mile race at Dover is scheduled to start just after 3:30 p.m. (et).