Which canon changes bother you about the NPC's here specifically? I didn't notice anything too egregious on first pass, but I'm not the most well-versed on RL lore, either. I'd ask mostly because I might like to use the old stories instead, if they're very different.
[MENTION=7635]Remathilis[/MENTION] lists off most of them. But I'll reiterate.
Madame Eva goes from being the head of the Zarovan branch of the Vistani to a non-Vistani. Which is odd given the Vistani can tell their own and don't like those of mixed blood or outsiders.
The ring of choking fog around the village of Barovia is gone and now surrounds the entire nation (which is smaller). The Vistani potion doesn't do anything.
VanRichten is a spellcaster/cleric when he was always presented as a rogue prior. And he lived centuries after the Ireena Kolyana incarnation of Tatyana. He's also very un-vanRichten, burning his books and planning the brutal murder of Vistani.
And the Morninglord cult was founded in the book
Vampire of the Mists well after Strahd killed his family at what I'm calling "the Black Wedding".
Now, canon additions are not a huge deal. Adding Baba Lysaga? Sure. Some werewolves in the woods, a winery, and chapel to St. Markov? Why not. Mother Night as an ancient Barovian goddess? Okay. Because these are additive and not revisionary.
But changing canon? No. Bad. Especially when it'd be easy to just accommodate the old canon with a single line.
Curse of Strahd does its own thing and just pulls classic names from the campaign setting and uses them for new characters. Like a bad episode of
Arrow where it brings in a classic DC character or concept as little more than an Easter Egg. Like they couldn't be bothered to do more than minimum research.
But the biggest slight is Strahd, who forms a pact with "Death" prior to meeting Tatyana, was already evil (being a conqueror and killing & mutilating a silver dragon), and already seeking immortality. Tatyana moves from becoming the tragic loss that drives him to evil and more the convenient excuse for murder. "Death" didn't approach him at his weakest when he was lamenting not being able to claim Tatyana and tempted him to darkness, but instead he actively sought them out prior to meeting her.
It changes his story from "I love my brother and family, but I will turn on them for you!!!!" to "Meh, I was gonna kill everyone anyway. Might as well get started." Which is a HUGE change.