It's a variation to 'This Magic Moment' done by Brett Sorrentino:
https://www.sencit.net/custom/
You can find a similar version here:
https://www.youtube.com/watch?v=7b7AzBPHkTg
HAHAHAHA! Nope. I knew that was too easy. It’s the second half of the trailer. Everyone on YouTube seems to think it’s M83’s My Tears Are Becoming A Sea. Any M83 fan can tell you it’s not. Damnit, I want that track so bad. Thanks for your efforts though. I appreciate it.