Well, one possible plot could be that Naruto is somehow transported to the DC universe where he meets Deathstroke. They might start as enemies because of their different moral compasses. Naruto, with his belief in friendship and protecting others, could see Deathstroke's mercenary ways as wrong. Then, through a series of battles and mutual understanding, they could end up working together to fight a greater evil that threatens both their worlds.
A plot could involve Deathstroke being hired to assassinate Naruto. But when he tries, he realizes Naruto is much more powerful and tenacious than he expected. Naruto, in turn, tries to understand why Deathstroke is after him. This leads to a strange alliance where they exchange skills. Naruto teaches Deathstroke about chakra and some ninja techniques, while Deathstroke shows Naruto some advanced combat and stealth tactics from the DC world.