How do I determine the valuation or value of the goods that I am importing?
"A "value for duty" must be declared for all goods imported to Canada in accordance with the valuation provisions of the Customs Act (the act), regardless of the circumstances of their importation. The value for duty is the base figure on which duty you may owe on your goods is calculated. Even if you do not owe duty, the value for duty of goods must still be established so that any applicable assessment of the goods and services tax, provincial sales tax or harmonized sales tax may be calculated."
Methods of valuation
Value for duty must be established using one of the six methods of customs valuation identified in sections 48 to 53 of the act:
Section 48 - transaction value method
Section 49 - transaction value of identical goods method
Section 50 - transaction value of similar goods method
Section 51 - deductive value method
Section 52 - computed value method
Section 53 - residual basis of appraisal method
You have to use the first of the six methods, the transaction value method, whenever possible to determine the customs value of imported goods.
If you cannot establish the value for duty of your imported goods using this first method, you must consider the alternatives in sequence and identify the method that is appropriate.
Into the USA:
"The Customs Valuation Agreement of the World Trade Organization (WTO) sets out a fair, uniform and neutral system for determining the value of imported goods on which customs officials levy duties. This system bars the use of arbitrary or fictitious customs values."
Methods of valuation
The Agreement states that the primary basis for the customs value of imported goods shall be the "transaction value" of the goods - the price that is actually paid or payable when the goods are sold for export.
Other Methods of Customs Valuation
For cases in which it is impossible to determine the transaction value of imported goods, the Agreement provides for other valuation methods. The first alternative is to set the customs value on the basis of the transaction value of identical goods sold for export to the same country. If there are no identical goods, the customs authorities shall use the transaction value of similar goods sold for export to the same country. If identical or similar goods are not sold for export to the same country, the value of identical or similar goods when sold in the importing country may be used. In the alternative, a computed value may be used; the Agreement describes how this value should be calculated. When all else fails, customs authorities shall use "reasonable means consistent with the principles and general provisions of this Agreement" to determine the value of the imported goods.
More reading: https://www.trade.gov/trade-guide-customs-valuation