It might be one of the house - elves. They are used to taking care of others and serving in the wizarding world. So an elf like Dobby or Winky could be the one feeding Harry. They would probably be very efficient at it, making sure Harry gets all the nourishment he needs while also keeping him clean and comfortable.
Maybe it's Dumbledore. In some fanfictions, Dumbledore is portrayed as a very father - like figure to Harry. Feeding Harry from a bottle could be a way of showing his deep care and protection for Harry in a different, more nurturing way than we usually see in the original series.
It could be Hermione. She is often portrayed as a caring and nurturing character. She might take on the role of looking after Harry in a situation where he needs to be fed like a baby.
Well, it might be a really strange and cute fanfic where Harry, perhaps as a baby or in a vulnerable state, is being fed a bottle. Maybe it's a story about taking care of a young Harry in an alternate universe where he's not in Hogwarts yet.
It could be a Death Eater in disguise. They might be trying to get rid of Harry once and for all to please Voldemort. They could have slipped the poison into his food or drink when he least expected it.
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.
He might meet international aurors. These are highly skilled wizards from different countries who are experts in dark wizard catching. They could teach Harry some new combat spells.
His friends from Hogwarts like Hermione and Ron would most likely support him. They have always been by his side through thick and thin in the original story, so in the fanfiction, they would continue to support Harry in his fight against the Ministry.
He could meet Fleur Delacour's family. Since Fleur is from France, her family might be an important part of the French wizarding community that Harry interacts with.
He could meet his future children, if he has any. They would likely be powerful wizards or witches with their own adventures. Also, he might run into the future versions of Hermione and Ron. They would probably be in important positions in the wizarding world, like Hermione might be a headmistress at Hogwarts or something.