According to Ubisoft CEO Yves Guillemot, Watch Dogs will hit store shelves in the first fiscal quarter. That means Watch Dogs will be available sometime between April and June 2014.
Here is Guillemot's full statement:
"Fiscal 2014-15 will see an exceptional games line-up, with the release of five major titles including Just Dance, The Crew and Watch Dogs, which is scheduled for release in the first fiscal quarter."