Personally i don't think Cancelo is trustworthy. Low mental skills and iirc injuries can also be a problem too, tho im not sure about the last one.
Semedo is a very solid option, usually cheap, consistent and you can easily profit if u find a better replacement. In one of my saves, the only experience of mine with Adriozola, he was Semedo's backup. Solid but not as good and specially not as consistent as Semedo.
Bellerín doesn't shine so much on AI's hands and seems too expensive for his skills. All said, Semedo is all around a better choice for me.
CB wise, u got great options. Pavard and Dias being the ones for not just now but the future, i'd stick with one of them. They're both great, Pavard being more of a Piqué style of player and Días... Puyol? Idk, he's a great player, a little agressive, way more then Pavard, but a great captain, mentally stronger then pavard although his tecnicalls are a little bit worst. I guess u just have to choose between a future captain with strong mentality or a more tecnicall CB. Really, u can't go wrong either way.
Between Koulibaly and Manolas, go for Koulibaly, easy choice.