It's in the Kanata Centrum, also known as the west-end shopping mall with the most poorly laid out collection of parking areas, small clusters of buildings, and through-ways.
Take your favorite route out to Terry Fox Drive, then go north until you cross the 417. Take your first right after the 417, which will bring you into the maze.
Turn right again onto a 1-way lane... then just keep your eyes open. Jack Astor's will be down there on your right somewhere.
Click
here to see the location on MapQuest.
I've also attached a quick 'n dirty pic of the location...