Any character can work in any LARP so long as you're willing to make it work in a way that makes sense within the game world. If it doesn't make sense and dealing with your character slams other players out of the mood and atmosphere that they're trying to enjoy than they're likely to become irritated and even avoid you. Characters that are obviously derived from pop culture can often irritate other LARPers because they tend to damage the fourth wall and remind people that this is a game because they rarely fit the game they've been ported into.
Altair is an awesome character from Assassin's Creed but that's because he fits the rest of the game quite well. He is an epic assassin and has a vibe that is exotic and generally confident which is fun to embrace but he also requires a fair bit of suspension of disbelief that is often inherent in high action genres. I mean, that man is obviously well-armed yet he can just step amongst a group of monks and blend in? Or leap multiple storeys into hay bales? That makes James Bond look realistic.
This isn't to knock Assassin's Creed or other tales in those genres. Its just that when you bring that character into the political turmoil of, say, Vampire: the Requiem, then you invoke all the wrong associations and burst other players out of their hard won atmospheric bubble. Not only that but if you want to do anything with the sort of smooth style of Altair than you're going to either be disappointed by the generally gritty and consequential Vampire tropes OR you're going to damage other people's enjoyment by enforcing a very different style of gameplay.
It's like if you were watching James Bond and he kept stepping into a Jane Austen-style romantic drama plot. It wouldn't make much sense and the two genres would fight it out tooth-and-nail until the whole thing was a chaotic mess. While you can have fun with that, ask yourself if that's the what your other players want? If so, fantastic. A game of clashing genres certainly would keep everyone's interest in how it all bangs together, especially when it careens into an entirely new genre.
If they wouldn't enjoy it, then why do it? Either you'll get disappointed (more likely as you're outnumbered by the other players) or they will be.
Even if your movie tie-in is from a compatible genre it's likely to dent the fourth wall as the other players are going to find it difficult not to think about that movie when they're dealing with you. Odds are you're going to want to add your own flourishes to the character and when you do that they may be distracted with thoughts of how that's not precisely how the actual character would have responded. The other trouble is that even if you pick a character from a movie that has similar tropes to Vampire, that character was designed for another plot and still may be a round peg in a square hold when ported over into the game.
Now that isn't to say that you can't take inspiration from movies and create quite a good character modeled off of them. That's what a lot of authors and screenwriters do. If you take Sherlock Holmes and port him straight into Vampire you'd have trouble as there's a number of assumptions built into his character (like the fact he's a good guy who wouldn't chill out with murderers) but that isn't to say that you couldn't play a high-humanity drug-addled investigator who plays the violin. Its simply that you'll get more buy in from other players if he's not called Durlock Foams, was Embraced in the Victorian Era yet behaves as though he were still a human from that time, and has a ghoul doctor as a companion who still treats him as a slightly baffling equal rather than his beloved master. Throwing in a ready-made genius nemesis that you've wrangled the Storyteller into creating for you is the final nail in the coffin as far as a straight port is considered.
Instead, take that high-humanity drug-addled investigator who plays the violin concept and work on it some more. When were they Embraced? The obvious answer is the Victorian Era but that's going to introduce a trade off - Victorian style (which does fit Vampire's genre conventions at least) ancillae (giving you more social and political clout and a longer history of successes) will clash with actually being the best in the business.
Humans tend to find it difficult to change their work methods often enough to stay up-to-date and vampire minds just aren't as malleable as human ones. Is your ancillae really likely to be the best in our world of forensic science and DNA analysis? Perhaps he still is simply through fancy footwork, a reliance on his powers of observation, and the ability to rely on certain vampire powers. Even so, how has he dealt with the fact that modern science has gone leaps and bounds ahead of him?
Perhaps he does have an assistant, but rather than be a professional medical doctor she's a forensic analyst and computer expert who likes to be on the cutting edge (bonus points if you can get another player to play this person). Perhaps he simply despises modern science for encouraging a lazy brain in order to disparage what is beyond his comprehension. Perhaps he joined the Ordo Dracul specifically to try to work on his kindred weaknesses in order to strive to stay up-to-date with science ... or perhaps he joined the Carthians and encourages them to goad him to modernising himself.
You can see how these choices will affect him, his personality, and how he deals with people?
If, on the other hand, you make him modern you can lay a further imprint on him. Perhaps he was with Research & Analysis in the Office of Strategic Services spying on the Axis in World War II in the Cover & Documentation Branch to ensure that spy equipment was perfectly authentic before switching over to X-2 Counterintelligence to use those same skills to deduce enemy spies and sabotage operations on Occupied soil. Now that's taking the core of the character (eccentric investigative genius) but giving it a very different vibe and thus making it more wholly your own. Besides, you now have an interesting back history that can pad out discussions amongst the court.
Or perhaps you make him all the more modern. He was Embraced quite recently, perhaps a few years ago, because his sire thought his skills were wasted on solving cases as a private investigator or even working in the Coroner's Office going over other people's paperwork.
Ironically enough, in the latter two examples you could have him nicknamed 'Sherlock' as it then becomes realistic to highlight his similarity to a fictional character. He isn't the Sherlock of the novels nor is that Sherlock based on him but he's probably the closest thing to a living Sherlock.
So how to personalise him more? Well, clan should be a big influence as should covenant. A Mekhet with Auspex could certainly provide the necessary knack with deduction but could take away from his own internal brilliance. A Daeva could explain his passionate eccentricities with him following his vices. Celerity could certainly make him a little closer to the fighter version from the most recent movies. Ventrue would justify his arrogance and the reason why he speaks quite formally (if you go with that). Gangrel and Nosferatu could give him an interesting quirk to deal with and take him down a very different direction. Now he has something to struggle against that will complicate his Requiem.
Did he pick his covenant? Was it his sire's choice? Did someone lure him in with false promises? Did he want what they had to offer? How has his covenant shaped him? What role has he fulfilled for them? The fictional Sherlock Holmes obviously didn't have to cope with kindred society or a covenant so it would certainly mould him to suit both you and the game better.
So, if you really want to play a movie tie-in be aware that both you and everyone else will get more fun out of it if you take the character's core components (especially the bits you like) and change it up a bit. Think about how they might be changed by different eras (and how that might work for you). Consider the influence of clan and covenant and a significantly changed history. Think about differences in mannerisms or skills that you might like to have.
In short, use that movie character as a launching point for you to breathe life into your own character rather than just stealing that character whole-sale.