Apparently, in Verizon's view, Canada is such a technologically backward nation that it costs an order of magnitude more to send data over their maple-syrup-soaked drunken-beaver-operated telecommunications system than it does here in the US.
There was no recourse; Verizon doesn't care why the bandwidth was used, even if it was unintentional. We canceled the contract.
EDIT: Contrasting point: for my Android, Verizon gives me unlimited data for $45/month. I use at least 1GB/month, and that's without watching videos or doing any other data-intensive stuff that I'd probably want to do on an iPad. (I don't pay the extra $20/month they want for tethering. I've found the Android is sufficient for my mobile computing needs.)