HOLLYWOOD (Variety) - Paul Giamatti and Alan Arkin have been tapped to round out the cast of FX's cable TV movie The Pentagon Papers, which begins shooting Sunday in Toronto.

They join star James Spader in the story of Daniel Ellsberg, the Pentagon consultant who in 1971 leaked a 7,000-page document detailing American missteps in Vietnam.

Claire Forlani, whose credits include Basquiat and the upcoming Jackie Chan actioner Highbinders, is close to signing on to play Ellsberg's wife.

Giamatti (Planet of the Apes, Big Fat Liar) and Arkin (Thirteen Conversations About One Thing) have signed to play Ellsberg's confidant Anthony Russo and mentor Harry Rowan, respectively.

The Pentagon Papers is slated for a December premiere.