2. Avengers Versus X-Men
Avengers versus X-Men is one obvious way to get the Marvel Cinematic Universe and X-Men franchises to bond and, given that Spider-Man is part of the Avengers team in this arc, he could join too. Interestingly, Wolverine is on the Avengers team in the arc and so is the Fantastic Four member Ben Grimm, so it could potentially mean characters who are currently owned by Fox joining up with characters currently owned by Marvel/Disney and Sony's Spider-Man to fight the X-Men. The main story occurs after Sam Alexander (Nova) crash lands on Earth and delivers a vague warning to the Avengers before lapsing into a coma. Iron Man deduces that the threat is the Phoenix Force and that it is returning to Earth and, at the X-Mansion, Wolverine tells Captain America that he believes the Phoenix is coming for Hope Summers. Captain America then travels to Utopia to ask Cyclops to hand Hope over to the Avengers so that they can place her into protective custody. Cyclops refuses, believing Hope to be the mutant messiah, and orders Captain America to leave. After a brief exchange, Captain America assembles the Avengers on Utopia and a battle ensues - starting with the Avengers storming Utopia after arriving on the S.H.I.E.L.D helicarrier - which then turns in to a global fight between the teams as they seek to find Hope, who has fled the scene (all while a team of Avengers attempt to stop the Phoenix in its tracks, to no avail, in space). Not only is it a very underrated story, it's also arguably the easiest way to merge these franchises as it explicitly requires the presence of the two main groups from two of them (the Avengers from the Marvel Cinematic Universe and the X-Men), while adding Spider-Man (legal issues aside) to the Avengers wouldn't be difficult at all. Thor, Iron Man, Hulk, Doctor Strange, Ben Grimm, Daredevil, Black Panther, Hawkeye and Wolverine et al going up against Magneto, Colossus, Storm, Cyclops, Namor, Emma Frost, Gambit, Rogue and Magik et al? In live action on the big screen? Yes please!