Getting Spider-man to join up with The Avengers at this moment in time would take a lot. It would require sony to give the rights, Marvel to fork over millions of dollars, or even some other alternatives. All this aside its still fun to think of how spidey could become one with the avengers despite being in an entirely different universe, so I present to you my Fun-time
So here we are in Amazing Spider-man 3 where they introduce some key characters for Sinister Six, Doc Ock, and Vulture.
In this movie we have a plot-line where Harry recruits two people to help him with his spider problem. Dr. Otto Octavius, a pioneer in the field of energy in this case, and Electronics Engineer Adrian Toomes, who is tasked with trying to revive electro in some way, with octavius tasked with helping him become stronger once he is revived
spidey catches wind of the new boys in town when oscorp tower is robbed of everything in special projects division by a man with 6 arms, dr octavius. in this robbery he obtains a big part of the original spiderman 2's plot, tritium, the last of it on earth
later on in the movie, vulture finds evidence of a very weak electro hiding within the power grid having been trapped in there after his physical body was destroyed
the only way to revive him is to create a massive source of energy from which he will be able to reform, the type of energy only a sun could supply, which is where tritium comes into play.
Having Figured Out The Plan, and knowing the possible reprocussions of such a thing spiderman tries to stop it from happening with unintended consequences
the movie ends with the reaction of the tritium occuring, otto succeeding and electro becoming whole once again, but he cannot stop it, seeing this he is forced to evacuate the building and spiderman shows up to see him in a panic
seeing doc ock they have their final battle which ends with doc ock becoming knocked out and spidey suck with a big reaction on his hands, and in a desparate attempt to stop it he breaks the machine surrouning it which does in the long run stop it, but in the short term it opens up a black hole in which spidey is sucked in and darkness...
he wakes up to find himself in new york, realizing he was not at the machine he desperately hurries to get to oscorp tower where the reaction was taking place only to find....it was replace by a strange similarly designed building with an A on the side, spidey was transported out of his own dimension and into the avengers
(Note: this period where he is gone is where the sinister six movie takes place showing their rise to power)
on his way to the tower he is greeted by the military who are currently occupying the manhattan area due to the recent ultron incident and they attempt to take spiderman into custody but spidey is to fast and swings away, having gotten away he wonders where he is and figures he just is in a different city....somehow.
but after swinging for a bit, and a couple run ins with criminals, and the law, he sees he knows these streets all too well, all except for one building, avengers tower...hoping for answers he goes to the source
after getting a while he makes it to avengers tower to find captain america,
( NOTE: fun red white and blue moment cuz why not )
after telling who he is, cap decides to introduce him to stark and banner who after hearing his whole story, deduce that he is from a separate universe but with no way of getting him back, he is stuck there, offered a place to stay at aveners tower, and a spot on the team after proving himself spidey accepts, seeing he better stick with people who know this new universe
Avengers 3: Rise Of Thanos Part 1
NOTE: i say part 1 because something like thanos and the inifinity gauntlet shouldnt be rushed in one movie, i will not go into detail with the avengers 3 movie (maybe in a different post) because this is about spiderman
in the final battle with thanos, spiderman is fighting alongside his teammates, but getting a bit to close to thanos, thanos decides spidey is a nuisance and uses the reality gem to send spiderman (yet again) to another dimention, more importantly, back to his own dimention with only one difference....new york is taken over by the sinister six.
this was just a fun little theory on how we could possible see spiderman join the avengers hope you liked, have any ideas or suggestion, let me know in the comments :)