There is a short and a long answer to this. The short answer is that a bill of sale or invoice is required to import shipments into Canada. On that bill of sale or invoice should show:

1.   Who the buyer and seller are
2.  What the items are
3. Where the items made
4. How much they cost – including currency
5. If applicable, a NAFTA certificate of origin is required for U.S. manufactured qualifying goods.

The long answer is shown in this 25 step by step of what is required on a proper Canada Customs Invoice – http://www.cbsa-asfc.gc.ca/publications/dm-md/d1/d1-4-1-eng.html