Another thumbs up for either "Sew Sisters" or "Hamels Fabrics"! I order regularly from both and am very pleased with both service and product. If you like pre-cuts, Hamels have a wonderful selection as well as fabric by the metre. As mentioned above, they also have a once a month sale of 20% off fabric by the metre (not pre-cuts). Sew Sisters often has really great sale prices too. And, I believe they both ship to the U.S.
Unless you can pick your order up on the other side of the border you take your chances on customs/brokerage charges which can be expensive. I have been told that Connecting thread send through Canada Post, so must give that a try.