For what was an incredibly well drilled and well equipped professional military the Germans were terrible at espionage and lacked a functioning intelligence gathering organisation, makes you wonder how they achieved as much as they did.
I don't believe Canaris was a double agent for one second, I accept that he was anti-nazi and did not follow their doctrine but I do believe he carried out his duties as well as he could which leads me to believe that he and his department were bordering on incompetent.
There is just too much that was missed by the entire German intelligence group (not just Canaris) to lead me to believe that it was not a deliberate plot to bring down the Reich.