Film is collaborative. In spirit anyway. It’s also an artistic industry, there’s a casualness to it. Forget what you learned in school about filling out a job application and just be polite. I’ve never started a query letter with the words “Dear Mr.” anything. If you’re querying a manager, this isn’t a future boss you’re writing to, it’s a future partner. Don’t be familiar, be yourself.
Hi John, I’m a writer blah blah blah vs Dear Mr. Amazing, can I kiss your ring? – which one sounds like the beginning of a working relationship and which one sounds like you’re establishing a hierarchy? Don’t under-evaluate your worth. Just because you’re the one asking to be read, doesn’t mean you’re indebting yourself. You’re looking for a mutually beneficial arrangement.
Also, some of these cats have pretty androgynous names. You don’t want to use the wrong honorific.