Practice Relating to Nuclear Weapons
Canada’s LOAC Manual (2001) states in its chapter entitled “Restrictions on the use of weapons”:
1. The United Nations General Assembly has condemned nuclear weapons as being illegal, although the international community itself is divided on this question. While nuclear weapons are not specifically prohibited by any international treaty, there is a strong argument to be made that the use of nuclear weapons would violate International Law on a variety of grounds including:
a. they would cause superfluous injury and unnecessary suffering;
b. their effect would be indiscriminate; or
c. their use would cause widespread, long-term and severe damage to the natural environment.
2. At the request of the United Nations General Assembly, the International Court of Justice (ICJ) issued an advisory opinion with respect to the legality of nuclear weapons in 1996. The majority of the judges ruled that the threat or use of nuclear weapons would generally be contrary to the LOAC and in particular the principles and rules of humanitarian law. However, the ICJ went on to state that it could not reach a final decision on whether the threat or use of nuclear weapons was illegal in extreme circumstances of self-defence where the very survival of a state is at stake.
3. When Canada deposited its ratification of Additional Protocol I, the following reservation was made:
“It is the understanding of the Government of Canada that the rules introduced by Protocol I were intended to apply exclusively to conventional weapons. In particular, the rules so introduced do not have any effect on and do not regulate or prohibit the use of nuclear weapons.” 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 526.
In 2003, in response to a question relating, inter alia, to the use of nuclear weapons, the Canadian Minister of Foreign Affairs stated that “we are opposed to the use of nuclear weapons or any weapons of mass destruction”. 
Canada, House of Commons Debates, Statement by the Minister of Foreign Affairs, 21 February 2003, Canadian Yearbook of International Law, 2003, volume XLI, p. 494.