Upload & Sell: On
The clerk is wrong. He definitely should declare the purchase to CBSA. If it exceeds his tax free limit, then he'll have to pay sales tax. Sometimes, they (CBSA) ask you to pay tax and a "blended duty" rate, which is bogus, because cameras and lenses from the US should be duty free, regardless of where they're made. He can quote this thread, if they dispute this blended duty issue. Of course, he can quote the B&H clerk if they notice that he imported an expensive, undeclared dohickey.
It used to be easy to get a refund of local taxes paid outside of Canada (esp. in the US, UK, and Europe), when you bring it into Canada. It's not so easy now, and I think it's not possible in many cases.
If you buy something online from B&H when you're in Canada, you don't have to pay NY taxes. In fact, they've (B&H) recently offered a new service where you pay the Canadian (provincial) sales tax and a reasonable handling fee to B&H at the time of purchase, and there are no extra fees when it gets delivered. In comparison with the alternatives (except for USPS, where in might fly under the radar), it's a good deal. OTOH, you have to pay for shipping.
P.S. lighting and other accessories might be subject to duty - just sayin'.