Hermione could be a likely helper. She's smart and resourceful, and she would likely believe Harry if he told her his reasons for escaping Dumbledore. She could use her vast knowledge of magic and spells to create distractions or to find ways to bypass Dumbledore's security measures.
Ron might also be there for Harry. Despite his sometimes bumbling nature, he has a strong loyalty to Harry. He could use his family's connections in the wizarding world. Maybe his older brothers have some useful magical items or knowledge that could aid Harry in his escape. For example, they could provide a magical map that shows hidden routes away from Dumbledore's detection.
There could be some new characters introduced in the fanfic. For instance, a rogue wizard who has been observing Dumbledore's actions from afar and has his own suspicions. This wizard could offer Harry a safe haven and teach him new forms of magic that Dumbledore doesn't know about, giving Harry an edge in his escape.
Well, perhaps Harry discovers some dark secret about Dumbledore that makes him feel he must escape. It could be that Dumbledore is being controlled by some dark magic and Harry realizes he's in danger around him.
One possible reason could be a misunderstanding. Maybe Harry overheard something that made him think Dumbledore was planning something against him that he didn't understand. For example, if he heard Dumbledore discussing a dangerous mission for him without his full knowledge.
Hermione would be a very likely character to help. She's smart and resourceful, and she would use her extensive knowledge of magic to come up with a plan for Harry's escape. Another could be Hagrid. He has a big heart and he's always been fond of Harry. He could provide a means of transportation, like his flying motorcycle or a secret passage he knows of. Also, Sirius Black might be involved. He's Harry's godfather and he would do anything to protect Harry from his family, so he could be a key figure in getting Harry out of that situation.
There's a chance he meets some magical creatures that can talk in the American wilderness. For example, he might encounter a Sasquatch that has a deep understanding of the ancient magic in America. They could form an unlikely friendship and the Sasquatch could help Harry in his journey to adapt to the new magical environment.
There could be a group of magical outcasts in Canada who take Harry in. These are people who have been shunned by the mainstream wizarding society for various reasons. They would understand Harry's need to escape and would protect him because they see him as one of their own, someone who is also trying to find a place where he can be safe and free.
One possible reason could be that Harry might feel he's been used too much in the past by Dumbledore. He could be tired of being thrust into dangerous situations without having a full understanding of the whole plan. For example, in the original series, he often felt like he was just following Dumbledore's orders blindly and it led to great personal risk and the loss of some friends. So in the fanfic, he might have decided enough was enough.
It's possible that an old acquaintance from Hogwarts who has family ties in America could assist him. This person might already have a network in America and could introduce Harry to important people. Also, there could be some reclusive magical scholars in America who, out of curiosity about Harry's powers and his role in the UK, decide to help him. They could teach him new magical skills that are specific to the American wizarding world.
Luna Lovegood could be a supporting character. She has an open - minded and unique perspective. She might support Harry in his defiance, understanding his reasons when others don't. Maybe she helps him see things from a different angle or provides some crucial information that validates his decision to defy Dumbledore.
It could be that Harry finds out about Dumbledore's secrets regarding the Deathly Hallows. If Harry thinks Dumbledore was more interested in the Hallows for his own purposes rather than for the greater good, it might make him hate Dumbledore.
Maybe Hagrid could help too. He has a special connection with magical creatures, and since Harry is in the form of an owl, Hagrid might be able to understand him better than others. He could provide a safe place for Harry to stay while they figure out how to turn him back, and he might know some old - fashioned remedies or magic that could be useful in this situation.