MIAMI (Reuters) - U.S. Defense Secretary Jim Mattis said on Thursday he was hopeful that the freeing of a kidnapped U.S.-Canadian couple and their three children in Pakistan was a harbinger for closer cooperation in the future.  This is a very positive moment and the Pakistan Army performed well,  Mattis told reporters on board a military plane, adding he hoped this would be  a harbinger for the future.   We intend to work with Pakistan in a collaborative way in the future to stop terrorism and that includes kidnapping,  Mattis added. He declined to comment on any specifics on how the hostages were freed. 