There could be some old family friends who come to see Harry at the manor. These friends might have known his parents well and can share stories about them. Also, it's possible that he meets some local witches and wizards who are associated with the Potter family. They could offer their help or give him warnings about the upcoming threats. And perhaps there are some magical beings like fairies or sprites that have made the manor's gardens their home and Harry encounters them during his stay.
He may encounter some of his father's old schoolmates. They might be there to pay their respects to the Potter family. They could tell Harry about his father's adventures at Hogwarts and how he was as a student. These encounters could give Harry a new perspective on his father and inspire him to be more like him in certain ways. Also, there could be some magical creatures that are guardians of the manor. Harry might meet them and have to prove himself worthy to stay in the manor.
He might meet the house - elves that have been taking care of Potter Manor for generations. They could show him around the manor and tell him stories about his family.
Maybe he discovers some long - forgotten family secrets. It could be something about his parents or the history of the Potter family that has been hidden away in the manor.
There's a chance he'll meet other outcast wizards. These wizards might have been shunned by the wizarding world above ground. They could be very different from the wizards Harry is familiar with, perhaps having their own unique styles of magic. They might initially be hostile to Harry, seeing him as an outsider from the 'normal' wizarding world, but later they could become his allies. They might also know secrets about the underground world that could help Harry in his future battles or quests.
He could meet other young wizards and witches who are also working summer jobs. Maybe some from other wizarding schools.
He could meet other fans of the same fictional universe. In some fanfictions, gay clubs are places where fans gather to discuss their favorite characters and storylines. So Harry might run into people who are also fans of his world.
He might meet his parents. Since they have passed away, the other side of the veil could be a place where they exist in some form.
He could meet a young and brilliant wizard inventor. This inventor is working on some newfangled magical gadgets and shows Harry some prototypes, like a self - flying broomstick that can change its shape according to the rider's mood.
Perhaps he'll meet an old patient who has been in the hospital for a long time. This patient could tell Harry some long - forgotten stories about Hogwarts in the past. There could also be a chance that he meets some other students who are also in the hospital for various reasons, and they might form a new friendship or alliance.
Perhaps he'll meet some interesting magical creatures that are native to the holiday location. It could be a friendly forest sprite or a wise old centaur. He may also cross paths with some international wizards who are also vacationing there and learn about different magical cultures from them.
He might meet Canadian witches and wizards. There could be a friendly wizard who shows him around the Canadian wizarding community.