With the MCU showing no sign of slowing down and only continuing to expand, and Wade Wilson hurtling towards it like a foul-mouthed, fourth-wall-breaking meteor, there are plenty of ways in which Deadpool can join up with the MCU stable of properties. In 2021 Kevin Feige confirmed that Deadpool 3 would be part of the MCU and that it will remain R rated, what remains to be seen is how the merc with a mouth is going to make his MCU debut.
While Reynolds has appeared in character alongside fan-favorite Korg from Thor: Ragnarok in promotion for Reynolds' film Free Guy, he's yet to make his official debut. How can Marvel capitalize on the success of the first 2 Deadpool films and use what worked in them to make a successful MCU debut for the character?
Deadpool is the king of meta and pop culture references. To bring him into the MCU, Marvel should lean into aspects of the first two Deadpool movies that made them great - self-referential humor and tacit acknowledgment of the studio restrictions on characters. The films have never shied away from calling out the restrictions on characters and studio politics. In the first film, Deadpool explicitly references how there is never anyone at the X-Mansion apart from Colossus and Negasonic Teenage Warhead, a reference he doubles down on in Deadpool 2 after Colossus drags him back there after Deadpools' repeated attempts at ending his existence.
During the scene, Wade expounds about the studio not throwing them a bone and wanting an appearance from just one X-man while the cast of the more recent reboot quietly shuts the door on him. Fleeting cameos like this are, although small, such a fun way to include audiences and get a laugh. In theaters, audiences cheered and clapped to see characters they knew existed in the same universe as Deadpool actively shut themselves out of the film.
The presence of the X-Men in Deadpool has become almost a trademark. Wade frequently mentions the X-Men and technically even joins the team as a trainee for approximately 5 minutes in Deadpool 2. Leveraging the X-Men connection would be a great way to segue both him and the mutants into the MCU proper. If Deadpool 3 continues the story from the first two films there's every chance that Colossus, Negasonic Teenage Warhead, Cable, and the others could follow Wade to The Avengers' doorstep.
Another almost constant companion to Wade in the films is the presence of Hugh Jackman's Wolverine. In both films, Wade has made reference to X-Men Origins: Wolverine where Reynolds played a rightfully maligned version of the character of Deadpool albeit briefly. In the second film, Deadpool even goes back in time post-credits to put an end to the original incarnation of himself in an actor of literal character assassination. He also goes back in time to kill Ryan Reynolds before he can sign on to Green Lantern which although harsh, is excellent fan service.
Deadpool 2 also features numerous other references to Logan. It opens on a music box diorama of Logan's death playing Air Supply's All Outta Love, features Wade monologuing about Wolverine riding his coattails when it comes to R ratings, and features a box of Wolverine themed cereal. Continuing to acknowledge the two characters' ties and rivalry will help to tie the two universes together, possibly helping to expand the multiverse angle for bringing in other Marvel characters into the MCU.
After concept art for Shang-Chi and The Legend of The Ten Rings revealed a look at Deadpool in the fight club, fans started to assume he had been cut from the film and that it was initially meant to be his way into the MCU. However, that rumor was quickly put to rest by concept artist Andrew Kim.
Now with Doctor Strange in The Multiverse of Madness on the horizon, speculation is rife that Wade Wilson is about to make his MCU debut straight from the multiverse. Ryan Reynolds has denied that he has any part in the film, but considering Andrew Garfield and Tobey Maguires' denial of their involvement in Spider-Man: No Way Home the only way to know for sure is to wait for the film's release in May.
Wade hasn't been shy in name-checking or mocking other characters in the MCU, he's referred to himself as Hawkeye after his powers were taken away in the Ice Box, inquired about Cables' Winter Soldier arm, and referenced Captain America while shooting a mobster in the head. All of these characters exist in the world of Deadpool and finally uniting them all on-screen should follow the tradition of what's come before - with Wade openly mocking them, annoying them, and refusing to actually work with them in a way that they would want despite his clear obsession with them.
Marvel also has to remember that the biggest asset they have in Deadpool is Ryan Reynolds. Reynolds has proven time and time again that he loves the character and wants to do him right (hence the Deadpool 2 post-credits scene). He also clearly knows what he's doing as his long-standing real-life "feud" with Hugh Jackman shows.