While it may seem like a long shot, Julian Dennison could be playing a gender-swapped version of Hope Summers, the first mutant born after the Marvel Comics events “House of M” and “Decimation.” Hope would go on to play a massive role in a trilogy of X-Book storylines over the course of three years, starting with “Messiah Complex” and ending with “Second Coming."
The big difference here, however, (outside of the character's gender), is that Cable is Hope’s protector. Their relationship is close to the one John Conner and the T-800 share in Terminator 2: Judgement Day, really, so it’s unlikely that Cable is this kid’s would-be assassin -- unless he’s taking on the role held by Bishop (who saw a future where Hope was a harbinger of destruction) in the aforementioned comic trilogy. The only real Hope connection that seems to hold any water is that, from what we’ve seen in the trailer, Dennison’s character seems to have some sort of power with relation to fire, which is tres Phoenix.
Another character Dennison may be playing is Evan Sabahnur, a cloned version of Apocalypse who, to put it lightly, has often been a point of contention for X-Force. Evan, also known as Genesis, was a target for the mutant assassination squad in the first arc of Rick Remender and Jerome Opeña’s Uncanny X-Force, “The Apocalypse Solution.” While this storyline didn’t include time travel (or Cable, for that matter) it did feature Deadpool heavily and toyed with the moral corrosion one would endure in make=ing the choice to kill a child in the hopes to avoid future devastation.
In many ways, Deadpool is the red-headed stepchild of the X-Men film franchise, but it did make a lot of nods to the films that came before it (meta and otherwise). Whether Deadpool and the other X-Films even take place in the same gonzo universe remains up for debate, but if they're even tangentially connected, then that means the character of Apocalypse has existed in some capacity. Having a bratty child clone of the character being hunted by a mercenary from the future who has seen what the kid is capable of actually makes a lot of sense (or at least as much sense an X-Men film can make). Taking this route would be a good way to combine several X-Force story lines from the comics, which allows for a wider range of characters who could be included in the film.
But the simplest answer is, maybe Julian Dennison is playing a character we’ve never met before. This would allow the film not to adhere to any of the storylines from the comics and give us something completely original. Yet, if this is the case, why don’t we have a name for the character yet? What are you hiding, Fox? Is he Morph?! Wait, please don't let him be Morph...
Debuting May 18, director David Leitch’s Deadpool 2 stars Ryan Reynolds as the titular Deadpool, Morena Baccarin as Vanessa, T.J. Miller as Weasel, Leslie Uggams as Blind Al, Brianna Hildebrand as Negasonic Teenage Warhead, Stefan Kapičić as Colossus, Zazie Beetz as Domino and Josh Brolin as Cable.