Well, it could be about Naruto having some of Deathstroke's combat skills. Maybe he has a more ruthless side in battles like Deathstroke. He might use his ninja abilities in a different way, combined with Deathstroke - like tactics.
Obviously, Naruto would be one of the main characters. And since it's about him being the son of Deathstroke, Deathstroke himself would be important. Also, characters from the Naruto universe like Sasuke and Sakura might still play significant roles as they interact with this new Naruto who has a different background.
One exciting plot twist could be that Voldemort discovers Harry's connection to Deathstroke and tries to use it against him. He might try to turn Deathstroke against Harry or use Deathstroke's enemies to attack Harry. Also, what if the Ministry of Magic finds out about Harry's true father? They could see him as a threat and try to expel him from Hogwarts. But then, it turns out that some of the Ministry officials are actually in league with Deathstroke's enemies, and Harry has to fight against both the Ministry and the dark forces. This would add a whole new layer of complexity to the story.
Well, in the traditional universes of Naruto and Green Arrow, it's completely impossible as they belong to different fictional worlds with their own established storylines and rules. Naruto is from a world of ninjas, chakra, and hidden villages, while Green Arrow is a DC Comics superhero in a world of metahumans and modern cities.
One possible plot could be that Naruto is found as a baby in the world of Green Arrow. Oliver Queen (Green Arrow) takes him in and raises him. Naruto grows up with a sense of justice like Oliver, but also has his own ninja - like tenacity. He might combine his natural ninja abilities (if he still has them in this crossover) with Green Arrow's archery skills to fight crime in Star City.