Mayer held an audience at the Air Canada Centre spellbound Monday night with a set that journeyed through his catalogue, with a surprise visit from Pickering’s Shawn Mendes. Nick Krewen John Mayer   At the Air Canada Centre, April 3, 2017 Fans searching for the perfect John Mayer concert may have come close to finding their slice of heaven at the Air Canada Centre Monday night. For nearly two and…