Commercial contracts are not created in a vacuum. In the event of a dispute, can parties adduce evidence outside the “four corners” of the document (e.g. prior drafts, negotiations) to support their interpretation?
As a starting point, the goal of every interpretative exercise is to determine objectively the intention of the parties at the time of execution based on the words chosen by the parties. To this end, courts are always entitled to take into account the commercial context, or surrounding circumstances, of a written agreement: Deserres v. Brault,  S.C.J. No. 36. This is so regardless of whether the contract is ambiguous.
The Lawyers Weekly, May 11, 2012
The Admissibility of Extrinsic Evidence