The Invoice template is a protected form. Click Tools > Protection and
select Unprotect Form. Now you can edit the cells for State and Zip. This
is a temporary fix for the current invoice.
If you need an Invoice template for Canada, you can find the Invoice
template (for Excel 2003) in c:\Program Files\Microsoft
Office\Templates\1033, called Sales Invoice.xlt. You can edit the template
and Save As a new template (e.g. Canadian Invoice.xlt).