After a junior career with Jokerit's under-18 and junior teams, Väänänen was drafted by the Phoenix Coyotes in the 1998 NHL Entry Draft as their second-round pick, 43rd overall. He remained in Finland to play with Jokerit in the professional SM-liiga for two seasons, winning a silver medal with the team in 2000 as runner-up for the Kanada-malja, the SM-liiga's championship trophy. Väänänen then joined the Coyotes in 2000–01 and recorded 16 points in his rookie season. In his fourth season with the Coyotes in 2003–04, he was traded at the trade deadline to the Colorado Avalanche in 2005 in exchange for Derek Morris and Keith Ballard. Due to the subsequent NHL lockout, Väänänen returned to Jokerit in 2004–05 and helped his former team to another silver medal, losing the Finnish championship to Kärpät. Returning to the NHL in 2005–06, he played two more seasons with the Avalanche before returning to Europe to play in the Swedish Elitserien for Djurgårdens IF during the 2007–08 season. On July 1, 2008, Väänänen signed a one-year contract with the Philadelphia Flyers. However, late in the 2008–09 season, on February 27, 2009, he was placed on waivers and claimed by the Vancouver Canucks. The move by the Flyers, which also included waiving Glen Metropolit, was precipitated by the imminent return of forward Daniel Brière from injury, requiring the club to dump salary to remain under the cap. On August 2, 2009, Väänänen joined national teammate Ville Peltonen, signing a one-year contract with Dynamo Minsk of the Kontinental Hockey League. He appeared in 52 games and recorded 6 assists as Minsk failed to make the playoffs in 2009–10. On May 3, 2010, Väänänen returned to Finland signing a contract with his original club, Jokerit, of the SM-liiga. On July 13, 2016, after six additional seasons with Jokerit, Väänänen retired from professional hockey, having been restricting to just six games due to injury in the 2015–16 season.
June 27, 1998 – Drafted in the second round, 43rd overall, by the Phoenix Coyotes at the 1998 NHL Entry Draft.
March 9, 2004 – Traded to the Colorado Avalanche from the Phoenix Coyotes along with Chris Gratton and a second-round choice in 2005 in exchange for Derek Morris and Keith Ballard
December 1, 2004 – Signed as a free agent by Jokerit.
July 1, 2008 – Signed to a one-year contract by the Philadelphia Flyers.
February 27, 2009 – Put on waivers by the Philadelphia Flyers, claimed by the Vancouver Canucks.