I've said for a long time that Ian Somerhalder could play Dante, he even kinda looks like him. I remember someone saying Chris Evans (years before the MCU lol) and I thought "Meh, maybe if it was DMC3 Dante" but now I think he could play an older Dante.
Nero, I'm not too sure, they need someone younger, with a good sense of humor. Maybe Robbie Amell (he could pass for a teenager or 20-something)
V? Adam Driver lol JK, all the people joking about how much V kinda looks like Kylo Ren (except really skinny). You know what, I'll agree with Z218's suggestion, Ezra Miller....Who also kinda looks like Adam Driver now that I think about it.
Vergil, well unless they get lucky with a pair of twins, whoever plays Dante, likely would also have to play Vergil, or change them to fraternal twins. Maybe Benedict Cumberbatch (if he played him like he played Khan in Star Trek: Into Darkness)
Lady, for some reason I wanna say Zooey Deschannel, could be cause I've had a crush on that woman since I was like 12, and picturing her as a demon hunting chick with a bazooka seems appealing to me lol
Trish, I'm thinking Karen Gillan. Strangely her roles in Jumanji 2 and Nebula in GOTG makes me think she could do it, like a mix of those characters.
Nico, I honestly don't feel like I know enough about her to try to cast her, may have some idea after DMC5 comes out.
Kyrie, I dunno, maybe Emma Watson