5. A Billionaire's Mad Dream
Very similar to the 'events taking place alongside' theory, another goes with the idea that a wealthy billionaire amassed the funds and personnel to help him/her create their very own Mass Relay. In the established canon, Relay's exist to transport considerable bodies of matter from one specific place to the next, so the idea is that having seen the oncoming Reaper threat, this anonymous billionaire had a Relay constructed, that takes him and his team to the Andromeda galaxy. To give the idea a little bit more credence, there is already the in-canon tale of Victor Manswell, another billionaire who embarked on an excursion in 2070 across the stars with 300 cryogenically frozen crew members. His story goes that they ran into an Asari ship and had a quite tense standoff of "What the hell are you?/No, what the hell are you!?" reactions, until the Systems Alliance calmed things down. Back to the theory, and it closes by saying you'd be playing as one of this rich guy's crew, but the main takeaway is that it still allows all the events of the trilogy to remain canon, albeit discussed vaguely in retrospect as the crew push forward.