You know, I thought I would hate any kind of shipping put in the show, comics, or just the canon. Especially with Luna, which is hands off territory. But after seeing what Big Mac deals with and how he thinks, I'm okay with this.
Luna, just after fighting Nightmare Rarity and getting over her final insecurities, as did Rarity, Luna decided to go full gamer Luna on us and enjoy competitions at the fair. ("Huzzah!") She picked out Big Mac to be her partner cause he looked strong and physically capable, and Big Mac didn't know what to think cause he was distracted by his original purpose, but over the course Luna said she really enjoyed his company as a strong, silent and reliable type, (much to the chagrin of her royal night guards) and Big Mac, even while distracted, enjoyed spending time with her as well.
After they parted ways for a while, at night Luna and Mac went on a farris wheel and Luna kissed Mac on the cheek, which really turned him on.
Also, the comic establishes that the 2 sisters have the advantages of all 3 races. Luna and Celestia's size is equivalent to earth pony strength. Luna is even stronger and faster then Big Mac even without wings, and when Celestia visited for an arm wrestling booth, Big Mac, who could pull a house, couldn't budge her hoof an inch. Unlike alicorns like Cadense or Twilight, they really are goddesses in every aspect.
Well that depends on your definition of god. By every aspect, you could consider Celestia more of a god then Thor from the marvel universe. Celestia has lived over 1000 years and controls the flow of the Sun AND Moon when she needs to. Granted, they live on a Narnian plane of existance and the Sun isn't nearly as big as it is on earth, but still. They don't age if they don't want to.
If you mean god by the definition of higher power, never aging AND can't be killed, that is open for debate. It is unclear whether Chysalis put her into a pod because 1) She couldn't be killed, or 2) She needed time to drain her of her powers. Her reason was to take over the world for her changelings, not destroy it by throwing it out of balance.
If you mean god by the definition of creation god, then that's a pretty limited definition of god in terms of a fantasy setting. I mean they've got Tartarus, the jail for the foulest demons, gods and immortal titans to ever roam the Greek fantasy realm.