"Can I get a menu?"
In a business, the boss has the higher status. As the one giving money to a person you have hired them to provide you with a service making you the boss; however, you are not the property owner, so as a customer your status to the employees is only slightly higher. Because of this, おねがいします, would be overly formal and less appropriate than ください, unless you are in a more formal restaurant and speaking with the owner (maybe the manager too), then ください MIGHT be a little too familiar. Feel free to tell me I'm wrong and explain why.
You have the nuances of the status badly understood, too. As a customer, for the purposes of the language and courtesy, you are very high status, as well as "out-group", and may well be addressed with 尊敬語, including the honorific suffix -sama 様 (technically suggesting you are royalty, or even of divine blood).
"Kudasai" [下さい] is a polite way of saying "give." It is used to show respect to the giver. The kanji, "下,"signifies "under" or "beneath" so the sentence actually sort of means "respectfully hand a menu down to me." It's technically an imperative statement however a better English translation is "may I please have a menu?" since that format is the most frequent way to request something. It should also be noted that although accepted and understood the kanji 「下」 isn't frequently used when writing "kudasai."