Question: Who starred as an undercover British agent in a movie with Kevin Joseph Zegers ?

Context paragraphs:
Fifty Dead Men Walking: Fifty Dead Men Walking is a 2008 English-language crime thriller film written and directed by Kari Skogland.  It is a loose adaptation of Martin McGartland's 1997 autobiography of the same name.  It premiered in September 2008, and stars Jim Sturgess as Martin McGartland, a British agent who went undercover into the Provisional Irish Republican Army (IRA), and Ben Kingsley as Fergus, his British handler.

The Spy Who Came in from the Cold: The Spy Who Came in from the Cold is a 1963 Cold War spy novel by the British author John le Carré.  It depicts Alec Leamas, a British agent, being sent to East Germany as a faux defector to sow disinformation about a powerful East German intelligence officer.  With the aid of his unwitting English girlfriend, an idealistic communist, he allows himself to be recruited by the East Germans, but soon his charade unravels and he admits to still being a British agent—a revelation that perversely achieves the ultimate objective of the mission.

The Man Who Stayed at Home (1914 play): The Man Who Stayed at Home is a play by J. E. Harold Terry and Lechmere Worrall.  First performed in 1914, the play is set during the First World War and tells the story of a group of German spies in South East England and the British agent who thwarts their undercover operation.  It ran for over a year and a half in London and became one of the longest running plays of the period.  It was also performed in Australia and New Zealand, and in North America where it was known as The White Feather.  There were two film versions of the play, the first in 1915 and the other in 1919.

River Patrol (film): River Patrol is a 1948 British crime film directed by Ben R. Hart and starring John Blythe, Lorna Dean, and Wally Patch.  The screenplay concerns a group of undercover British customs officer who investigate a gang of nylon smugglers.  It was made by Hammer Film Productions as a supporting feature.  It was made at Marylebone Studios in London.  It is notable for being one of the earliest films made by Hammer following its relaunch after the Second World War.

British Agent: British Agent is a 1934 espionage film directed by Michael Curtiz and starring Leslie Howard and Kay Francis.  It is based on "Memoirs of a British Agent", the 1932 autobiography of R. H. Bruce Lockhart, who had spent a number of years working for the British Secret Service.  The film was produced by First National, which was then a division of Warner Bros..

Kevin Zegers: Kevin Joseph Zegers (born September 19, 1984) is a Canadian actor and model.  He is known for his roles as Alec Lightwood in "", Josh Framm in the "Air Bud" film series, and Damien Dalgaard in the CW teen drama "Gossip Girl".  He also starred in the films "Dawn of the Dead" (2004), "Transamerica" (2005), "It's a Boy Girl Thing" (2006), "The Jane Austen Book Club" (2007), "Fifty Dead Men Walking" (2008), and "Frozen" (2010).

Jack Tar (film): Jack Tar is a 1915 British silent war film directed by Bert Haldane and starring Jack Tessier, Eve Balfour and Thomas H. MacDonald.  An Admiral's daughter goes undercover in Turkey to help a British agent thwart a German plot during the First World War.

Attack on the Four Square Laundry: The Attack on the Four Square Laundry was a Provisional IRA ambush in the Twinbrook area of Belfast against a special British Military unit known as the Military Reaction Force.  At least one undercover British soldier (Edward Stuart (20)) was killed, the IRA claimed they killed 5 undercover soldiers altogether.  The attack took place on 2 October 1972.

Brian Robinson (loyalist): Brian Robinson (c. 1962 - 2 September 1989) was a loyalist from Belfast, Northern Ireland and member of the Ulster Volunteer Force (UVF) who was witnessed murdering a Catholic civilian.  His death as a result of an undercover British Army unit is unique as it is one of the only deaths from the alleged shoot-to-kill policy in Northern Ireland which involved a loyalist victim.

Basra prison incident: The Basra prison incident was an event involving British troops in Basra, Iraq.  On 19 September 2005, two undercover British Special Air Service (SAS) soldiers disguised in Arab civilian garments and headdresses opened fire on Iraqi Police officers after having been stopped at a roadblock.  Two Iraqi officers were shot, at least one of whom died.  The two British men were arrested and taken to the Al Jameat police station.

Supporting paragraphs: Kevin Zegers Fifty Dead Men Walking
Answer: Jim Sturgess