It depends on the vendor and whether they are registered to collect taxes in your province or perhaps just the GST portion. If so, they will charge you the tax, if not, it is up to you to report the transaction and pay the tax in your home province - although I can't think of anyone I've ever met who does this, they just buy on-line out of province and save their money...
You don't pay US or NY tax...but you will most likely have to pay GST when the items arrive....probably PST as well.
There is no 'duty' on photographic equipment coming from the US, but you may have to pay 'brokerage' fees etc. I have found that it's much cheaper if you have packages sent via the US Postal Service, than with a courier like UPS or FedEx.