I am not a lawyer and did not play one on TV.

A brief trip through Google-land leads me to the understanding that a product whose Country of Origin is China/HongKong and is imported into the US via a third country (Canada) that product is still subject to the Chinese Tariff requirements.

And since the de minimus exception has been removed for Chinese goods they are still taxable (tariff is a tax), even though cost less than $800 USD.

If the sum value of the shipment is greater than $800 you may also be liable for the additional 10% tariff from Canada (exceeds the de minimus exception)..