I have been buying from B&H for more than 15 years. Absolutely no problems, that weren't handled quickly and professionally. My purchases over that time period total several 10's of thousands... I think I have enough experience to offer an informed opinion.
Most purchases of a photographic nature are not dutiable, you will however have to pay GST and provincial taxes (if applicable where you live). Some items, bags being an example that comes to mind, are potentially dutiable since they are considered "bags" rather than "photographic accessories."
Years ago I used to have to coach B&H sales staff to correctly describe the items on thier commercial invoices to ensure that they were correctly classified for duty purposes. That hasn't been the case for years, as they now do an excellent job of classifying and documenting the goods so that they sail through customs with nary a problem.
The savings can be substantial, even with current exchange rates, and the availablility of many items is rarely matched at the price by Canadian retailers. If you haven't already I would check out Vistek in Toronto (
www.vistek.ca) and "The Camera Store" in Calgary (
www.thecamerastore.com). Pricing here can be quite competitive, although either will be hard pressed to match the selection at B&H.
Hope this helps.