The reviews are in

James Travers:

Once there were reasons for the costly, long and deadly Canadian commitment to Afghanistan. Now there are none.
...
Canada's reasons for its blood and treasure offerings to Afghanistan have never been quite what they seemed or exactly as first Liberal and then Conservative governments explained. Creating a model democracy and civil society from warring factions and feudal customs is a softly engaging narrative that gains veracity through repetition. It's not the hard-headed stuff that persuades prime ministers to put their political hegemony at risk by putting lives in harm's way.
...
(I)n politics and war, triumphs are fleeting. Bowing to U.S. pressure to continue a losing battle won't appreciably improve cross-border relations now shaped as much by domestic economics as international threats. Any extension of the combat mission beyond 2011 would jeopardize current military success by demanding more than can be sustained by a small force already stretched too thin.

Whatever the motivations for going to Afghanistan, Canada has no compelling reason to stay longer.