A mysterious old wizard who has been watching Harry from afar could be the one to give him the 'tr'. This wizard could have seen the potential in Harry and decided that the 'tr' was the key to unlocking Harry's full power. The wizard might be an ancient figure who has ties to the founders of Hogwarts and has a vested interest in seeing Harry succeed in his mission to defeat Voldemort.
Hermione might give it to Harry. She is always researching and stumbling upon strange and wonderful magical items. She could have discovered the 'tr' in the library or during one of her side - quests for knowledge. Knowing Harry's importance in the battle against evil, she gives it to him, believing that he will be able to figure out its uses better than anyone else.
There's a possibility that it's a mysterious figure from a different wizarding school. This person could have heard of Harry's reputation and journey. They might give Harry the trivet as a sign of alliance or as a test. They want to see how Harry will use this strange object. Maybe this figure is from a school that has a different approach to magic, and the trivet is a symbol of that different magical culture.
Lupin could be a likely candidate. Given his experience and his role as a sort of mentor figure to Harry, he could give Harry the talk. It might involve Lupin sharing his own experiences with being a werewolf and how to deal with secrets and prejudices in the wizarding world.
Perhaps 'tr' is a time - turning relic. Harry Potter gets it and is faced with the moral dilemma of whether to use it to change past events. He might consider using it to save his parents, but then realizes the potential consequences of messing with time. This could lead to a whole adventure where he has to make difficult decisions and also face the Time - Turner's side - effects, like being in two places at once in a confusing way.
It could be Luna. Luna is known for her unique and often unexpected gifts. She might give Harry a hair tie that has some special meaning, like it was made from a rare magical plant.
It could be an old and reclusive wandmaker who has a special connection with Harry. Maybe this wandmaker sees potential in Harry that others don't and decides to create a custom wand for him.
It could be his loyal owl, Hedwig. She might be staying with him in the attic, providing comfort and also being a messenger for him when he needs to communicate with his friends outside.
Well, in fanfiction, Neville Longbottom could be one of the visitors. He and Harry could exchange gardening tips as they explore the manor's gardens. Additionally, Dumbledore's portrait might be magically transported to Potter Manor, and he could offer his wisdom and guidance to Harry as he lives in the manor. And of course, Hagrid might come with some magical creatures to show Harry, adding more excitement to the manor.
His friends from Hogwarts, like Ron and Hermione, are likely to help. Ron could bring his family's practical knowledge of wizarding homes and Hermione would contribute with her extensive research skills.
Hermione would be a great help. Her vast knowledge of magic and books could provide the necessary information for building the planet, like the right spells and magical theories.
He might meet Canadian witches and wizards. There could be a friendly wizard who shows him around the Canadian wizarding community.