TORONTO -- A dramatic thriller about controversial WikiLeaks founder Julian Assange will open this year's Toronto International Film Festival while hotly anticipated features from directors Steve McQueen, Denis Villeneuve, Justin Chadwick and Matthew Weiner will make world premieres.

British actor Benedict Cumberbatch stars as the infamous Assange in "The Fifth Estate," the Bill Condon-directed film that will kick off the star-studded Toronto fest on Sept. 5.

Cumberbatch is also among the stars of McQueen's "12 Years a Slave," which tells the true story of a free black man who was kidnapped and sold into slavery in 1841 and features turns from Chiwetel Ejiofor, Michael Fassbender, Paul Dano and Paul Giamatti.

Festival director Piers Handling says he was struck by the number of films that deal with issues of freedom, noting that Chadwick's "Mandela: Long Walk to Freedom" with Idris Elba will also debut at the fest.

"It's so much about people fighting to liberate themselves," Handling said following a press conference Tuesday that revealed big-name gala and special presentations.

"I mean that's what Mandela is all about. We're showing a film on Lech Walesa, of course that's what the fight that he led in Poland is all about. (With) Julian Assange it's all about freedom -- freedom of information, freedom of access."

New films from directors Atom Egoyan, Alfonso Cuaron, Jason Reitman, Mike Myers and John Wells are also headed to the festival, widely regarded as a key platform for Oscar hopefuls.

Wells has stacked his family dramedy "August: Osage County," with A-listers including Meryl Streep, Julia Roberts, Ewan McGregor and Sam Shepard. It's based on the Pulitzer Prize-- and Tony Award--winning 2007 play.

Meanwhile, Cuaron helms the 3D thriller "Gravity," which stars Sandra Bullock as a brainy medical engineer who embarks on her first shuttle mission with help from an astronaut played by George Clooney. It will also open the Venice International Film Festival, starting Aug. 28.

Reitman's "Labor Day" casts Kate Winslet, Josh Brolin and Tobey Maguire in a tale about a 13-year-old and his mother who unwittingly taking an escaped convict into their home, while Egoyan will debut "Devil's Knot," based on the true story of three teens dubiously convicted of killing three children in a small Arkansas town. It stars Reese Witherspoon, Colin Firth and Kevin Durand.

Canadian director Don McKellar scores a prestigious gala slot for his Newfoundland-set film "The Grand Seduction," an English-language remake of the 2003 Francophone film, "Le Grande Seduction." It centres on a small town desperate to lure a doctor so that it can also get a factory, with Taylor Kitsch as the wooed doctor and Brendan Gleeson as a villager who does everything he can to make him stay.

Myers, meanwhile, makes his directorial debut with "Supermensch The Legend of Shep Gordon," a documentary about the wild life of the veteran music executive, who is also a longtime pal of Myers'.

The fest will close with director Daniel Schechter's "Life of Crime," featuring Jennifer Aniston and Mos Def. Based on an Elmore Leonard novel, it's described by Handling as "a very light, fluffy crime caper."

In the past, organizers traditionally picked a Canadian film to kick off the festivities, but more recently they have looked internationally for buzzy titles with emerging stars.

The DreamWorks film "The Fifth Estate" is especially timely and should get people talking, says Handling.

"Over the last five years I guess we've shown four international and one Canadian (film). Traditionally we used to open with a Canadian film. I think we're open to anything at this point in time but we wanted to have the freedom to just invite anything," he says.

"If there's a film of that kind of stature that we are excited about we would definitely open with a Canadian film but this year we are opening with 'Fifth Estate' and we're delighted."

The 11-day festival will also mark the world premiere of Villeneuve's "Prisoners," which stars Hugh Jackman as a father pursuing his missing six-year-old daughter with help from a detective portrayed by Jake Gyllenhaal.

Other potential highlights include: Montreal director Jean-Marc Vallee's "Dallas Buyers Club," a fact-based drama about an HIV-afflicted Texas electrician starring Matthew McConaughey, Jennifer Garner and Jared Leto; "Third Person" from London, Ont.-born director Paul Haggis, which follows three couples in three cities and stars Liam Neeson, Mila Kunis and James Franco; and "You Are Here," the feature-film debut of "Mad Men" creator Weiner that stars Owen Wilson and Zach Galifianakis as childhood friends who struggle to handle a large inheritance.

Handling says Canadian directors Villeneuve and Vallee have each grown into "incredible filmmakers."

"And both of them I think have made films that I think will surprise people," he says.

"We've followed Denis since he was a young filmmaker, the same with Jean-Marc, so it's wonderful to see them arrive in the international stage. Jean-Marc closed the festival a few years ago with 'The Young Victoria,' Denis's been here a number of times before with a film. (They are) two of the supreme talents working in Canada."

The festival will also feature the directorial debuts of several well known-actors, including Joseph Gordon-Levitt's "Don Jon," Keanu Reeves' "Man of Tai Chi" and Jason Bateman's "Bad Words."

One of the last performances by James Gandolfini will also be unspooled, when Nicole Holofcener's comedy "Enough Said" makes its world premiere. The "Sopranos" star, who died last month, plays the love interest of a divorced woman played by Julia Louis-Dreyfus.

The Hollywood Reporter reports that another posthumous release comes by way of "All The Wrong Reasons," an ensemble drama co-starring late "Glee" star Cory Monteith as a department store manager. Festival organizers would not confirm whether the film will join the lineup.