The Northeast Grand Prix will feature the GTD Pro and pro-am GTD classes only, with no prototypes present at the tight Connecticut road course.
Gunn claimed his second IMSA pole and will head the field after logging a best effort of 50.593s in the frantic 15-minute qualifying session, in which with traffic posed issues for several drivers.
The #23 HoR Aston beat fellow Briton Jack Hawksworth in the #14 Vasser Sullivan Lexus RCF by 0.191s.
Corvette Racing's Antonio Garcia posted the early benchmark as the first driver under the 51-second bracket, but the #3 C8.R's track record was soon eclipsed to leave the Spaniard third on the grid.
Behind Jules Gounon's WeatherTech Racing Mercedes, the #9 Pfaff Motorsports Porsche 911 GT3 R completed the five-car Pro field after Patrick Pilet had a moment over the kerbs through the chicane.
Mike Skeen topped the GTD runners aboard the #32 Korthoff Motorsports Mercedes, trailing just behind the five Pro entries.
Skeen's pole lap was 51.157s, but Frederik Schandorff's #70 Inception Racing McLaren 720S GT3 EVO of Frederik Schandorff was just 0.007s slower.
The GTD points leading #1 Paul Miller Racing BMW M4 GT3 had a difficult qualifying in Madison Snow's hands to languish ninth in class and will start 14th overall in Saturday's 20-car field.