Here is Givony's defensive reel on Kanter. Not sure how much stock to put in it being a high school game. We don't know the score, his team could have been winning by 30 points and even in the NBA you see guys take plays off then.
https://www.youtube.com/watch?v=Mu96EoByub8
How does this NOT show an agenda with Givony? How can you take the opposite of a highlight reel and give it anymore credence than a highlight reel. I'm sure, if he wanted to, he could have put together a highlight reel that made Kanter look like a defensive monster.
From what I've seen, I'd call Kanter a slightly below average defender (not bad, just not an 'average' NBA PF/C). However, he does have the tools and desire and I believe he'll easily become average. He's a great scorer and an elite rebounder.