I have a company that wants to manufacture my product in Canada, then ship back into the US. What taxes or duties will I have to pay to cross the border with this product?
Average cost of each product is $120,000 Ca.

What is the product? Customs duties depend on the type of goods

For most high tech items such as this there is no duty you would simply have to pay sales tax on the item. Have the purchaser ask their customs broker but generally machines and electronics are duty free items.