Keanu Reeves began training for this film four months before filming. He says, "There are so many different kinds of action sequences, not only more styles of martial arts and more gunplay, but also motorcycles, horses and dogs, so the training was intense. But honestly, I love it. I love this character and I love the John Wick universe we've created."
(at around 16 mins) Early on, Wick finds himself in a room filled with revolvers from the 19th century. Desperately, he swaps parts of the revolvers, listens to the mechanisms as he spins the cylinders and cocks the different hammers. This is a homage to the scene in The Good, the Bad and the Ugly (1966), when Tuco is assembling a revolver to suit his taste from a multitude of other revolvers in a gunsmith's shop.
From the trailer and the movie: "Guns. Lots of Guns." Neo (Keanu Reeves) says these same words in The Matrix (1999).
(at around 21 mins) Keanu Reeves was asked if he did his own stunts when John Wick was hit by the cars and he responded by saying, "Well, I would've, but you know, hospital. I could've maybe done it once, but that would've been it for me."