Actually, Khadr was in Guantanamo as of 2003, under the Chretien and then Martin governments.

The 'abuses' of his Canadian rights occurred on two occasions, in 2003 and 2004, well before the Harper government came to power.  

The Supreme Court was quite clear in its final decisions that Khadr's rights did not extend to mandatory repatriation to Canada, which is consistent with what other Canadians who run afoul of the law in foreign countries experience.

Chretien intervened for Khadr's father in 1998 when Khadr senior was involved in bombing an embassy in Pakistan.  In turn, Khadr burnt that favour to a crisp by joining and aiding the most senior of al-Queda folks including those involved in 9/11.

Little wonder that Chretien, Martin or Harper would want to go out on a limb for another Khadr.