Règle correspondante
Canada
Practice Relating to Rule 20. Advance Warning
Canada’ LOAC Manual (1999) states:
An effective advance warning shall be given of attacks which may affect the civilian population, unless circumstances do not permit such a warning to be given. For tactical reasons, an attacking force may not give a warning in order to maintain the element of surprise. 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, p. 4-4, § 29.
Canada’s LOAC Manual (2001) states in its chapter on targeting:
An effective advance warning shall be given of attacks which may affect the civilian population, unless circumstances do not permit such a warning to be given. For tactical reasons, an attacking force may not give a warning in order to maintain the element of surprise. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 420.