This whole thing was initiated by the board of Hollinger not Fitzgerald. An internal investigation determined that he and others had received improper payments. After this the board of Hollinger called for his resignation. Then Hollinger filed suit for recovery of the money. It was about a year later, largely based on evidence uncovered by Hollinger, that criminal charges were filed.

When ordered to return them, he did so tout de suite and right speedily.

He returned the boxes about a week after the video of him removing them was made public. What if anything was removed from those boxes in not known.

In that security video at 10 Toronto Street, Conrad Black may be doing all manner of things, but he’s not tampering with any witnesses.

Tampering with evidence fits the statute just as well as tampering with witnesses.
If some other criminal were to shred all evidence of their criminal wrongdoing would you also think that they should not be subject to obstruction charges provided that shredding was done in Canada or Mexico?