With respect, you are glossing over the crucial differences:

Arar's detention was a direct result of Canadian actions, 

Khadr's was the direct result of actions against a Canadian ally and he was jailed by the US.

Canada had no part in initiating Khadr's detention or anything that flowed from it -- that was a direct result of Khadr's own actions.  The visits from Canadian authorities weren't even permitted until well after a year of his imprisonment, and to your point about honest mistakes, there is no evidence to suggest that Canada requested that Khadr be sleep deprived before his initial interviews, nor is there any evidence to suggest that the conduct of those interviewers in 2003 & 2004 (when the breaches occurred) exacerbated the situation that Khadr created for himself.  His beef should be with the US.

As Khadr is the first case of treason post-Charter, the situation should have been fully adjudicated by the courts.

In no way should his compensation have equaled Arar's.