He might have a very different view of magic. Wonderland has its own strange and chaotic rules, so Harry would grow up with a more surreal perception of the magical world. For example, he might be used to things changing size randomly like in Wonderland, and when he comes to the normal wizarding world, he could be quite confused by the more 'orderly' magic there.
His magical abilities could develop in a very unorthodox way. In Wonderland, the laws of nature are so different. He might learn to use magic in ways that are more about manipulating the chaotic environment rather than the traditional spell - casting in the wizarding world. For instance, he could use magic to navigate through the constantly changing landscapes of Wonderland.
One challenge could be controlling the assassin's violent tendencies. Since the person is being groomed to be an assassin, it's likely they have a natural inclination towards violence, and Harry has to find a way to temper that while also teaching self - defense.
No. The idea of Harry Potter being involved in such a situation goes against the values of the original series. The Harry Potter series is mainly about magic, friendship, and fighting against evil. This kind of fanfic concept not only distorts the characters but also involves inappropriate and unethical content.
Most likely very negatively. The Harry Potter fan community values the positive aspects of the series. They would see this fanfic as a disrespect to the original work and its characters.
He'd be more disciplined. His character would be shaped by military values. He'd be less likely to act impulsively and more likely to think things through strategically.
Harry's character would be more attuned to the deeper magics. He would be less likely to jump into things without thinking. Since Flamel is a master of alchemy, Harry might be more interested in the scientific aspects of magic. He would also have a greater respect for life and magic's power, as Flamel, with his long life, would instill in Harry a sense of wonder and caution about the forces they deal with.
It could be that the assassin was initially a victim of some dark wizard's experiment. Harry, being the hero he is, feels responsible for the child and decides to raise him. In the process of raising, he unknowingly nurtures the assassin-like qualities in the child because of the unique circumstances and challenges they face together.
Obviously, Harry Potter himself. Then there could be some Canadian - born witches and wizards as his friends. Maybe a tough - as - nails girl from the Yukon who is an expert at ice magic. And a laid - back boy from Vancouver who has a special talent for communicating with magical forest animals.