World number one Serena Williams is eager to test herself against the world's best, including Wimbledon champion Marion Bartoli, at the WTA Tour's Rogers Cup that starts on Monday.

Williams won the tournament the last time it was held in Toronto in 2011. It shifted to Montreal last year, where former Wimbledon champion Petra Kvitova defeated China's Li Na in the final.

Now that it has returned to Toronto, Williams is hoping a victory in the $2.369 million event can boost her build up to the final Grand Slam of the season, the US Open at Flushing Meadows.

"It was just such a confidence boost to win such a big tournament, such a staple," she said of her 2011 victory.

"It was very good for my confidence and it definitely gave me the experience I needed. It propelled me to get to the finals at the US Open," added Williams, who lost the final at Flushing Meadows that year to Samantha Stosur.

The 31-year-old American brings a formidable recent record to the Canadian hard courts, with seven titles this year including a French Open crown and, most recently, the Swedish Open.

However, she thinks there could be plenty of room for improvement, and more titles.

"I don't know if I've peaked yet," Williams said as she prepared for this week's tournament. "I don't know if I've gotten to the top of the mountain yet.

"If I am there, I want to stay there."

That's ominous news for her challengers, many of whom will also be in Toronto.

They include two-time reigning Australian Open champion Victoria Azarenka, seeded second, who reached Sunday's final in Carlsbad in her first tournament since returning from the knee injury that forced her out of Wimbledon after one round.

Azarenka, of Belarus, is the only player in the last six months to beat Williams on hardcourts -- at Doha in February.

By reaching the Carlsbad final she ensured she'll regain the world number two ranking, supplanting Maria Sharapova who is among the missing this week with a nagging hip injury.

Poland's Agnieszka Radwanska is seeded third and Li fourth.

Italy's Sara Errani, Kvitova, Bartoli and Angelique Kerber round out the top eight seeds.

Both Li and Bartoli are playing for the first time since Wimbledon.

Since Wimbledon Bartoli had pulled out of the tournament in Stanford with a hamstring strain suffered en route to her emotional first Grand Slam title.

Caroline Wozniacki, Roberta Vinci, Maria Kirilenko, Sam Stosur, Kirsten Flipkens, Sloane Stephens and former world number ones Jelena Jankovic and Ana Ivanovic are seeded ninth through 16th.

There are also a few Grand Slam champions scattered among the unseeded players -- Francesca Schiavone in Williams' section, Svetlana Kuznetsova in qualifying and Venus Williams, a seven-time Grand Slam champion and former world number one who will be playing her first tournament since Roland Garros.