The interesting question of how the Geneva Conventions apply to detainees taken by Canadian troops in Kandahar and then handed over to Afghan authorities is the subject of this post by colleague Wherry.
Here’s what I take to be an authoritative answer from inside the Department of National Defence, from the consistently helpful Feb. 6, 2009, report of the military Board of Inquiry into In-theatre Handling of Detainees:
“The Government of Canada’s position is that those parts of the Geneva Conventions and additional Protocols related to Prisoners of War are reflective of customary international law, and will apply to the conflict with Al Qaeda and the Taliban, even if they do not apply as a matter of treaty law.
“Common Article 3, so called because it appears in Geneva Conventions I – IV, provides the minimum standard of care, stating: In the case of an armed conflict not of an international character occurring in the territory of one of the High Contracting Parties, each Party to the conflict shall be bound to apply, as a minimum, the following provisions…(1) Persons taking no active part in the hostilities, including members of armed forces who have laid down their arms and those placed hors de combat by sickness, wounds, detention…shall in all circumstances be treated humanely… The Parties to the conflict should further endeavour to bring into force, by means of special agreements, all or part of the provisions of the present Convention. 
In support of this position, the CDS on behalf of the Government of Canada, entered into an arrangement with the Government of Afghanistan for the transfer of detainees.  This arrangement provides that the participants will treat detainees in accordance with the standards established in the Third Geneva Convention, designed to protect Prisoners of War.”