This is from the Old Navy customer service site "Shipments to International Addresses
At this time, we are unable to accept or ship international orders."
That is too bad - I am wearing an entire outfit of their clothes right now - I really love them. If you live close enough to the US to make a trip in, it might be worth finding one of the few Old Navy's that have maternity clothes in the store.
Motherhood Maternity has a Canadian site http://www.motherhoodcanada.ca/
Their clothes aren't too bad - I have some I really love and some I really hate.
If you want to spend a bit, I think Isabella Oliver would ship to Canada.