Brooks Koepka arrived at this week's Canadian Open as the star attraction but said he does not really care about his result as long as he leaves with his game sharp ahead of next week's U.S. Open.

Two-times defending U.S. Open champion Koepka has played the week before each of his four major championship victories, and is happy to use the preceding event as a tune-up for the bigger stakes that follow.

"It doesn't really matter about the result. I couldn't care less what happens," the American said on Wednesday at Hamilton Golf and Country Club in Ontario, a comment that will not win any prizes for diplomacy.

"It's just how I feel I've played, am I hitting enough good shots and really finding a rhythm?

"I just want to feel good going into next week."

The U.S. Open runs from June 13-16 at Pebble Beach, where the 29-year-old has a chance to become the first player in over a century to win the tournament in three consecutive years.

Koepka had two weeks off after winning the PGA Championship at Bethpage last month, and says he did not touch a club during the fortnight, preferring to relax before hopefully playing his way back into form in Canada.

"As long as I can leave feeling confident, striking the ball very well, starting it where I want to, finishing where I want to, hit some good putts, it doesn't matter if they go in or not, I just want to feel confident leaving."

The Canadian Open is the world's third oldest national championship, first played in 1904, and it has a bumper field this year after moving to an earlier timeslot in the schedule.

Defending champion Dustin Johnson is playing, Rory McIlroy makes his first appearance, while Justin Thomas is teeing up as he plays his way back from a wrist injury that caused him to miss the PGA Championship.

Officials have presented a Hamilton course with plenty of rough, which prompted a thumbs up from Koepka.

"I think it's actually a perfect set-up for next week," he said.

Dustin Johnson shot a 6-under 66 in the final round last year to win the Canadian Open at Glen Abbey. This week's tournament is at Hamilton Golf and Country Club. (Frank Gunn/Canadian Press)

A couple of key changes have stacked the odds against Dustin Johnson as he tries to defend his Canadian Open title.

The No. 2 golfer in the world pulled away from the field after a nearly two-hour rain delay to win his first Canadian Open last year, firing 6-under 66 in last year's final round to finish at 23 under. But this year the only Canadian stop on the PGA Tour has moved from Glen Abbey Golf Club, a course Johnson is familiar with, to Hamilton Golf and Country Club.

More importantly, the tournament has moved up in the golf calendar, making it a lead-in event to the U.S. Open and drawing a significantly stronger group of competitors.

"I mean, it's a really good field. It's a golf course I haven't played. That definitely adds a little bit more difficulty to it," said defending champion Dustin Johnson on Wednesday. "I don't know the golf course as well as I know Glen Abbey, where I played a lot of Opens."

"This isn't just a preparation week. This is a very prestigious tournament, one of the oldest tournaments in the world that I would dearly love to be able to add my name to," said McIlroy, who has never played a competitive tournament in Canada. "I'm fully focused on this week, but knowing that if I play well here, this week, and have good control of my ball and my distance control, that will serve me well going into next week. "

One problem for Johnson, Koepka and McIlroy is that none of them had a chance to play a full practice round. Due to off-site sponsor obligations and a pro-am tournament on Monday, they were half-round as part of a pro-am on Wednesday.

"I like the front nine. It's the only nine I've seen, but yeah, I like the golf course," said Johnson, whose brother Austin serves as his caddy. "(Austin) went out Tuesday and kind of looked at it. He's good enough now where he can got a pretty good beat on the course."

That lack of familiarity may give the 26-player Canadian contingent a brief edge, at least for the first round.

MacKenzie Hughes, who has played Hamilton Golf and Country Club numerous times, says that familiarity will be an advantage during this week's Canadian Open. (Nathan Denette/Canadian Press)

Mackenzie Hughes of neighbouring Dundas, Ont., has played Hamilton dozens of times. Corey Conners of Listowel, Ont., took in a practice round in May and Adam Hadwin of Abbotsford, B.C., played in the Canadian Open when it was last in Hamilton in 2012.

"I think it's a huge advantage. There's an added comfort level, just knowing the course and knowing what to expect," said Conners. "I'm really happy that I got the chance to play a few weeks ago. I got a plan together and to be familiar with the terrain, know what to expect and just definitely an added comfort level for the Canadians."

A total of 26 Canadians will be competing for the national championship. No Canadian has won the event since Pat Fletcher in 1954.

On top of the 20 that were announced in the final field on Friday, James Allenby of Langley, B.C., Thomas DeMarco of LaSalle, Ont., Etienne Brault of Mercier, Que, and Toronto's JC Deacon all qualified on Monday at Heron Point Golf Links in Alberton, Ont.

Albin Choi and Richard Lee, both from Toronto, were also late additions to the field with exemptions.

"We all — I've been in here probably four, five, six years in a row now — and all we've talked about is 1954," said Hadwin. "Until one of us does that, I think it's going to hold a lot of value for us."