Actually, they can because the shopping cart allows them to but Ancestry won't actually ship it to you and they won't refund your shipping charge. Unbelievable. This is their exact statement...
"Please do not order from Ancestry.com as we do not ship to Canada due to International shipping and customs issues. Try not to sign up on Ancestry.com as the price is in USD and if the price ever increased you would have to pay that increase. If you already ordered from Ancestry.com it will take about 30 business days or you may not receive the items ordered. Shipping cost is non refundable if you needed a refund."
If you won't ship to Canada then why do you allow people to put in a Canadian address including country = "Canada" in your shopping cart.