From what I saw of him last season at Inter, he’s a surprisingly aggressive tackler (a bit of a yellow card magnet too) but he needs to work on and improve his positioning, got caught out a few times last year. If Allegri can eliminate those mistakes out of his game - wow.
He can't defend well. But good coaching might change that plus the support and help from our defensive organisation. Emre Can will liekly be the man protecting "his side". Cancelo got all the tools to be a good defender, it's whether or not he'll be able to follow tactical instructions and be disciplined in 95+ minutes.
Spalletti is not the coach to get defenders to shine defensively, so I would leave my judgement until 6-12 months into his Juventus stint.
A good upgrade on MDS and with age on his side could be a great signing for the future. Really hope he can fulfil his potential here. Team starting to take shape for next year....