As I responded a couple of ours ago to https://community.verizonwireless.com/t5/iPhone-X-Xr-Xs/Canada/m-p/1120940#M3184 :
What plan do you have? Do you have an International Plan? Have you looked at TravelPass? Some plans include Canada and Mexico for calls, text and data. If not, adding TravelPass will trigger a $5/day charge and use your current plan rates when used in Canada (or when hitting a Canadian tower close to the border).