Both are correct. Your grammar book will have several pages on this topic. Briefly, the simple present and present continous can be used for "scheduled" future events (which are viewed as certain to occur). The simple present usually applies to transportation and the present continuous usually applies to people. Examples: "My plane leaves at 0920 on January 3, 2019." (several months from now, but I have a ticket, so it is scheduled future event) "My wife and I are leaving on January 3, 2019 and we are returning on January 17." The near future and near future continuous (going to <verb>) can be used for planned near future and far future events (which are viewed as certain or probable). Examples: "After supper, I am going to read a book." "My sister is going to marry her boyfriend in January." The near future can also be predictions about the near future. Example: "The clouds are dark. It is going to rain soon." The simple future and simple future continous (will <verb>) can be used for intended future events (which are viewed as general intentions without a plan). Examples: "My wife will visit her sister next summer." (A general intention). There are additional uses of the simple future such as to make a decision or to make a promise. The future simple is also used as a generic tense for a future activity (certain, planned, or intended). For more information, consult a grammar book.

You can use present continuous to express future circumstances that have been arranged or are mutually understood. (We are having a meeting next week at three.) In the case of your sentences, the meeting is already confirmed, the information is simply being relayed. I think both are correct, and the only difference I can find is tense.

Hi there, He "will" be having a meeting is definitely the most suitable and correct sentence to use. That is because "will" is often used to indicate things that happen in the future. If you eliminate it from the sentence, like how you did with sentence one the meaning appears to be ambiguous and unclear, so we might as well just include "will".