Nearly a decade since its launch, Grand Theft Auto 5 still holds the distinction of being one of the most successful open-world games ever made. Much of the game's popularity has been bolstered by GTA Online, of course - its online multiplayer portion that launched just two weeks after its original debut on the Xbox 360 and PS3.
But GTA Online wouldn't be what it is today if the single-player game hadn't introduced players to its enormous sandbox, a fictionalized version of California called San Andreas. Just as important as the setting itself was the intertwining stories of its three main protagonists, Michael, Franklin, and Trevor. That story had culminated in a third act where you have to make a very important choice, which in turn begs the question: which of its three endings is considered canon? To answer this, we must first take a look at each possible ending and how the canonical version ties into post-game events.
Note: There will be spoilers for the events in Grand Theft Auto 5 ahead.
The Setup
Following Michael, Franklin, and Trevor's successful heist on the Union Depository, Franklin is approached by FIB agent, Steve Haines. Steve orders Franklin to kill Trevor, who he views as both a threat and liability to the FIB due to his psychopathic ways. Subsequently, Franklin is also approached by the business tycoon, Devin Weston, who instead orders Franklin to kill Michael for interfering in his affairs.
This leaves you with three choices, each with wildly different outcomes. You can choose to kill Trevor as instructed by Steve Haines, kill Michael for Devin Weston, or opt to kill neither and instead join them to fight off all the people who want them dead. Depending on which of the three options is chosen, you are forced to deal with the consequences, details of which are as follows.
Kill Trevor
Choosing to kill Trevor triggers the mission Something Sensible in which Franklin meets with Trevor to discuss their problems. While Trevor is complaining about Michael being the source of those problems, Franklin points his gun at him in disagreement. Trevor manages to escape in his truck, after which a car chase ensues.
Franklin receives a call from Michael offering help and the latter soon arrives. Together, the two men are able to cause Trevor's truck to crash into a fuel tanker. Trevor stumbles out of the car wreck, crawling through fuel as he laments the betrayal of both men. At this point, the player can either choose to shoot Trevor or wait for Michael to finish him off instead. The fuel ignites, burning Trevor alive, before the tanker eventually explodes, killing him.
Kill Michael
Choosing to kill Michael triggers the mission The Time's Come in which Franklin meets with Michael to discuss their problems. While they are talking, Michael soon catches on that Franklin had been sent there to kill him, prompting him to escape in his car. Franklin gives chase and the two men end up at the Palmer-Taylor Power Station, where Michael begins to climb a generator tower.
Franklin is eventually able to catch up with him and the two men engage in a tussle that ends when Franklin pushes Michael over the edge. He catches Michael in time to save him from the fall, having experienced a change of heart. But Michael was very much aghast at the betrayal, promising to take Franklin down with him. The player can either choose to let Michael go or pull him back up, with either option ending with a still defiant Michael falling to his death.
Deathwish
Choosing to kill neither Trevor nor Michael triggers the mission The Third Way in which Franklin goes to Lester for help. Lester comes up with a plan to lure out the FIB's strike team and mercenaries from Merryweather Security, who Franklin, Lamar, Trevor, and Michael defeat after a prolonged firefight. Trevor then goes to kill Steve Haines, while Michael goes after Stretch, and Franklin handles Wei Cheng.
After the three antagonists are successfully taken out, Trevor storms Devin Weston's mansion, killing all his guards before capturing him. He then rendezvous with Franklin and Michael at the Chiliad Mountain State Wilderness. There they dispose of Devin by pushing the car in which he had been stashed into the sea. The car explodes, killing Devin. Franklin, Michael, and Trevor take a moment to revel in their victory against their enemies before going their separate ways.
Which Ending Is Canon?
Of the three possible endings in Grand Theft Auto 5, the Deathwish option is considered canonical. This is primarily supported by events in GTA Online, which serves as both a prequel and sequel to the events depicted in GTA 5.
In GTA Online, Trevor Philips is referenced multiple times. Most prominently, a photo of him and Mrs. Madrazo (a character featured in GTA 5) having an affair can be seen at the end of The Cayo Perico Heist. Since the story in that mission is set well after those depicted in Grand Theft Auto 5, it can be deduced that Trevor Philips was still alive and the Kill Trevor option is not canonical.
In addition to this, the events of the Deathwish option are directly referenced in the GTA Online mission, Casino - Strong Arm Tactics. In it, the son of GTA 5 antagonist Wei Cheng, Tao Cheng, mentions almost getting killed at the Pacific Bluffs Country Club. This was the same place Franklin had ambushed Wei Cheng in GTA 5 before killing him. He'd however spared his son, Tao, who now runs the family business, confirming that the events of the Deathwish option are indeed canonical.