Cañas was born in Buenos Aires and named after Argentine tennis star Guillermo Vilas.

[4] Cañas had won the first ATP level title of his career that season, in Casablanca, and reached the final of three other tournaments.

In addition to this, he reached the fourth round of a Grand Slam tournament for the first time, achieving this result on two occasions, at the French Open and Wimbledon.

Cañas's path to the final saw him defeat a renowned set of players, including world number two Marat Safin, and top-ten ranked Yevgeny Kafelnikov and Roger Federer.

[4] No traces of any other forbidden substance were found in Cañas's sample, and the player asserts the diuretic was present in some medicine prescribed by ATP doctors Mercader and Chinchilla for a cold he contracted during the Acapulco tournament in Mexico.

He was allowed to return to full professional activity from September 11, 2006, and the money prizes acquired before the suspension was restored.

This double victory made him the only player (besides Rafael Nadal) to have defeated Federer in consecutive tournaments since 2003.

To get to the final, Cañas defeated Tim Henman, Juan Carlos Ferrero, Richard Gasquet, Roger Federer, Tommy Robredo, and Ivan Ljubičić, respectively, before losing to Novak Djoković.

He now runs his own tennis academy in Aventura, Florida along with former tour pros Martín García and Gustavo Oribe.

Cañas played a defensive counter-punching game from the baseline, using his retrieving skills in order to frustrate opponents.