Wade Wilson's pansexuality is one of the few major differentiators between him and the DC character he directly parodies, Slade Wilson, a.k.a. Deathstroke—the others being the cancer storyline and postmodern fourth wall awareness.
Much was made of Deadpool's pansexuality in the lead-up to the first movie, and rightly so. In the typically heteronormative worlds of comic book characters, Deadpool's sexuality has always been an anomaly. This is by design, according to a series of tweets from co-creator Fabian Nicieza. "[Ambiguous sexuality] has ALWAYS been a part of [Deadpool's] makeup," said Nicieza. That hasn't stopped homophobic revisionism among an unfortunate subset of Marvel fans.
Still, some critics, and even Ryan Reynolds himself, want to see more of Deadpool's ambiguous sexuality onscreen. Reynolds has been pulling for Deadpool to explore what Nicieza calls the "omnisexual, pansexual, heterosexual, homosexual, etc. aspects of [his] character" in the sequel; specifically, Reynolds wants Deadpool to find a man in Deadpool 2. Thus far, the cinematic Deadpool's non-heterosexual interactions have been either flirtations or threats…with the exception of that scene with the unicorn.