Practice day on Friday saw Fernando Alonso bring his Ferrari around Circuit Gilles Villeneuve with the fastest time in the morning practice, only to see the Hamilton and Rosberg dominate the afternoon session in their Mercedes AMGs.
"The Ferraris looked quite close today and the rest of the field seemed closer in general, but hopefully not too close," said Hamilton. "It's very hard to overtake here, so pole position is important.
"Nico looked very quick as well, so I have my work cut out for sure. We'll find out everyone's pace in qualifying (Saturday) afternoon, so let's wait and see what happens."
Hamilton thrives on the tightly-cornered 4,361-kilometre circuit, and the superior power of this year's Mercedes engine makes the Briton and his German-Finnish teammate Rosberg heavy favourites to stretch their winning run to start the Formula One season to seven races.
Hamilton is a three-time winner in Montreal, and will be gunning for his fourth pole position in qualifying. Rosberg is looking for a second pole and a second win in a row after a victory at Monaco two weeks ago.
"It felt pretty good out there, but we've still got improvements to make and there is more to come from the set-up and balance," said Hamilton. "We're not quite where we want to be yet."
Hamilton posted a quickest lap of one minute 16.118 seconds, just ahead of Rosberg at 1:16.293.
Defending champion Sebastian Vettel's Red Bull car was third at 1:16.573 followed by the two Ferraris, Kimi Raikkonen in 1:16.573 and Alonso in 1:16.701.
"I'm still a tenth off the quickest time so I'll work hard with our engineers to find that extra pace," said Rosberg. "It's a unique track here, and it's very difficult to hit the curbs just right."
The Mercedes team has been all-but unbeatable since the switch to more fuel-efficient 1.6-litre turbo engines this season.
They have won every race, with Hamilton taking four and Rosberg two, and have finished one-two in the last five.
There has been more competition between the teammates than with the rest of the grid so far, but perhaps the track's peculiarities, and it's lurking dangers, will make a race of it on Sunday.
The circuit features long straightaways leading into sharp turns. There are chicanes, including one near the home stretch that has sent many top drivers into the concrete barrier known as the Wall of Champions.
"It is a short lap here, which closes up the field anyway, but it feels like Ferrari might be pushing us harder this weekend," said Mercedes executive director Toto Wolff. "We will need to get every detail right to deliver our potential in the race, so there's plenty of work still ahead of us."
Alonso caused a mild surprise by beating the Mercedes in the morning practice session, but Rosberg topped the Spaniard's time of 1:17.238 early in the afternoon runs. When the Mercedes drivers switched to supersoft tires 30 minutes into the afternoon, they were too quick for the field.
The two-time world champion Spaniard, a winner in Canada in 2006, is a distant third in drivers standings behind the two Mercedes but it is still early in the 19-race season. He said this week his car is improving, even if the gap with Mercedes will be very difficult to close.
"It's going to be tough," said Alonso. "There are updates coming to the car that we've been working on for some weeks.
"All these hopes, we need to see it on the track. It's one of the shorter circuits, so we expect the times to be really close. So we need to find perfection. One or two tenths can be six or seven positions. We need to be in the front of those cars."
The large crowd that turned out on a cool, overcast day got its first earful of the new F1 engines, which no longer have the high-pitched whine that was the sport's signature sound for years. Instead, it's a much quieter rumble.
Jacques Villeneuve, the 1997 F1 champion and a native of Iberville, Que., has no problem with the sound.
"The problem with the engine isn't the volume," said Villeneuve. "It's good.
"You can bring your kids and you know that you won't blow their eardums. That's a good thing. You can have a phone conversation. The problem you can feel that there's no power. There's no grunt. If you look at the turbos in the 1980s, the volume wasn't really louder, but you could tell the drivers were fighting with a wild animal. That's not the case now."
A dicey moment came 27 minutes in when Adrian Sutil had to take a short cut over a curb to avoid crashing into Kevin Magnussen's slow-moving McLaren. Stewards investigated the incident and decided it did not warrant a penalty.
However, Red Bull's Daniel Riccardo was given a reprimand for passing Pastor Maldonado's Lotus in "a manner potentially dangerous to others" in pit lane. It was the Aussie's first reprimand of the season.
Jules Bianchi of Marussia hit a wall hard and sustained heavy damage in the morning practice but the French driver felt he would be will be OK afternoon. But after three laps his Ferrari-powered car stayed in the garage most of the afternoon.
Caterham had 22-year-old American Alexander Rossi in Kamui Kobayashi's car for the first practice, although the Japanese driver took over in the afternoon session.
Rossi, a GP2 driver being groomed for F1, was last in the 22-car field at 1:21.757, just behind teammate Marcus Ericsson. Rossi will also drive in practice at the United States Grand Prix in Austin, Texas in November.