Those sentences pretty much mean the same: the intent is to stay in a good hotel, next holiday. The tone of voice, emphasis placed on words, and context of the conversation would give the cues on whether the reservation has been made -- or whether the speaker is informing someone else that "this reservation must be made or I will be very angry."
For example, as we leave the hotel that was far away from the convention we were attending (which was in another hotel), I tell my husband, "Next year, we will be staying in the convention hotel!" The reservation has not been made, but he knows that it better get made as soon as possible, or I am going to fuss at him a lot!
Later, if I am calmly telling a friend, "Next year, we will be staying in the convention hotel," my tone of voice (and lack of emphasis) indicates that I have no doubts about this, which would imply that the reservation has been made.