In clear but windy conditions, Braun – who shares his CORE autosport-run Oreca LMP2 with Jon Bennett – set the early pace around the fearsome Canadian road course at 1m08.693s, before lowering the fastest time with 1m07.475s and 1m07.155s efforts.

His quickest lap was 0.916s faster than the first of the Penske-run Acura DPis of Dane Cameron, who circulated in 1m08.071s. Filipe Albuquerque was third fastest in the leading Cadillac, the #5 Action Express car he shares with Christian Fittipaldi, on 1m08.088s.

Jonathan Bomarito was a late improver in the #55 Mazda DPi on 1m08.152s, jumping to fourth at the expense of Felipe Nasr in the #31 Action Express Caddy, and beating his 1m08.254s.

The second Acura of Ricky Taylor/Helio Castroneves was sixth fastest in Taylor’s hands. The Watkins Glen-winning JDC-Miller car of Stephen Simpson and Misha Goikhberg was only seventh fastest, 1.4s off the pace.

In GTLM, Earl Bamber was the leader of a Porsche 1-2 lockout in his #911 RSR on 1m14.538s, half a second clear of Nick Tandy in the #912 sister car.

The Chevrolet Corvettes were next up, a couple of tenths down on the Porsche pace, with Jan Magnussen heading Oliver Gavin by less than a tenth.

Chip Ganassi Racing's pair of Ford GTs were fifth and sixth, Dirk Muller ahead of Richard Westbrook, with the BMWs slowest in the class.

Bill Auberlen was fastest in GTD on 1m16.848s in his Turner Motorsport BMW M6, but only by a fraction of a second from Jack Hawksworth’s Lexus. Jeff Segal was third fastest in the #63 Scuderia Corsa Ferrari 488.

Practice results:

Pos.	#	Drivers	Class	Chassis	Time	Gap
1	54	Jon Bennett   Colin Braun	P	ORECA LMP2	1'07.155
2	6	Juan Pablo Montoya   Dane Cameron	P	Acura DPi	1'08.071	0.916
3	5	Christian Fittipaldi   Filipe Albuquerque	P	Cadillac DPi	1'08.088	0.933
4	55	Harry Tincknell   Jonathan Bomarito	P	Mazda DPi	1'08.152	0.997
5	31	Eric Curran   Felipe Nasr	P	Cadillac DPi	1'08.254	1.099
6	7	Helio Castroneves   Ricky Taylor	P	Acura DPi	1'08.267	1.112
7	99	Mikhail Goikhberg   Stephen Simpson	P	ORECA LMP2	1'08.580	1.425
8	10	Jordan Taylor   Renger van der Zande	P	Cadillac DPi	1'08.583	1.428
9	85	Simon Trummer   Robert Alon	P	ORECA LMP2	1'08.685	1.530
10	22	Pipo Derani   Ryan Dalziel	P	Nissan DPi	1'08.810	1.655
11	77	Oliver Jarvis   Tristan Nunez	P	Mazda DPi	1'09.023	1.868
12	52	Gustavo Yacaman   Sebastian Saavedra	P	Ligier LMP2	1'09.049	1.894
13	38	James French    Kyle Masson	P	ORECA LMP2	1'09.842	2.687
14	912	Earl Bamber   Laurens Vanthoor	GTLM	Porsche 911 RSR	1'14.538	7.383
15	911	Nick Tandy   Patrick Pilet	GTLM	Porsche 911 RSR	1'15.031	7.876
16	3	Jan Magnussen   Antonio Garcia	GTLM	Corvette C7.R	1'15.276	8.121
17	4	Oliver Gavin   Tommy Milner	GTLM	Corvette C7.R	1'15.357	8.202
18	66	Joey Hand   Dirk Müller	GTLM	Ford GT	1'15.709	8.554
19	67	Ryan Briscoe   Richard Westbrook	GTLM	Ford GT	1'15.835	8.680
20	24	John Edwards   Jesse Krohn	GTLM	BMW M8 GTE	1'16.177	9.022
21	25	Connor de Phillippi   Alexander Sims	GTLM	BMW M8 GTE	1'16.331	9.176
22	96	Bill Auberlen   Robby Foley	GTD	BMW M6 GT3	1'16.848	9.693
23	15	David Heinemeier Hansson   Jack Hawksworth	GTD	Lexus RC F GT3	1'16.929	9.774
24	63	Jeff Segal   Cooper MacNeil	GTD	Ferrari 488 GT3	1'16.980	9.825
25	14	Kyle Marcelli   Dominik Baumann	GTD	Lexus RC F GT3	1'17.078	9.923
26	33	Jeroen Bleekemolen   Ben Keating	GTD	Mercedes-AMG GT3	1'17.083	9.928
27	44	Andy Lally   John Potter	GTD	Audi R8 LMS GT3	1'17.128	9.973
28	93	Justin Marks   Lawson Aschenbach	GTD	Acura NSX GT3	1'17.161	10.006
29	16	Wolf Henzler   Michael Schein	GTD	Porsche 911 GT3 R	1'17.179	10.024
30	58	Patrick Long   Christina Nielsen	GTD	Porsche 911 GT3 R	1'17.294	10.139
31	86	Alvaro Parente   Katherine Legge	GTD	Acura NSX GT3	1'17.315	10.160
32	48	Bryan Sellers   Madison Snow	GTD	Lamborghini Huracan GT3	1'17.444	10.289