Yeah I wouldn't cancel that pre order just for the chance they have one at store. Which probably won't happen anyways unless your in a big city then there who knows. As Mathieu said the phone is hard to come by and if u cancel it could be months before you get one.
If you ordered an iPhone 7 Plus then definitely do not as Apple has come out and stated that neither the Jet Black iPhone 7 or any iPhone 7 Plus models of any color will be available in store anywhere in the entire world. Apple back at it again making fake shortages to increase demand SMH.