I suppose I should pop in here and mention something that has been said before but is worth repeating.
This is true for Canada and quite likely for other countries as well.
If buying from a US-based online shop, be sure that your fabric will be shipped by USPS (the Post Office), not FedEx or UPS. The reason is that you may be assessed large brokerage fees if dealing with FedEx or UPS.
Be advised too that the flat-rate envelopes commonly used for international shipping are NOT trackable when sent by USPS Priority Mail International. Packages sent by UPS, FedEx, or Express Mail ARE trackable. My perception is that most people assume that all packages are trackable and it just isn't so.