I received an ITA and am filling out my application online. I believe they need a scan of the stamp from our last entry into Canada. I've searched every page of my passport and am certain that there is no stamp of entry from when I entered through the Niagara/Buffalo crossing by bus. I can see the stamp from US immigration for when I entered the US but nothing from the Canadian side when I came back. Should I be concerned that my application will be rejected because this is missing?