The Treaty on the Prohibition of Nuclear Weapons goes much further than simply banning the possession of nuclear weapons on a nation's own soil. It prohibits a range of activities—the transfer, deployment, stationing, or stockpiling of nuclear weapons under any circumstances. Also, it broadly prohibits any party to the treaty from assisting, encouraging, or inducing another state to engage in prohibited activities.
This means that any state that chooses to ratify the ban treaty would immediately find itself unable to support, for instance, NATO's nuclear sharing arrangements, which are a critical element of NATO's nuclear deterrence that extends to all allies, including Canada.
For these reasons, the nuclear ban treaty is fundamentally incompatible with the collective defence commitments that Canada and its allies have made and regularly reaffirmed since the founding of NATO.
That being said, a pillar or cornerstone of NATO's nuclear policy is that nuclear disarmament and non-proliferation are a core element of NATO's and Canada's approach to nuclear deterrence as well. It's a core part of our policy, and it has been restated and reaffirmed, for instance, in the Warsaw summit communiqué and in the North Atlantic Council's statement on the nuclear ban treaty.
In that statement we reiterated—and I don't want to get too lawyerly here—article 6 of the NPT that talks about the step-by-step and a verifiable way of achieving nuclear disarmament. Canada is actually leading one of the most viable channels to move that step-by-step approach to disarmament forward, the fissile material cut-off treaty. That's outside of NATO, obviously, but we're still firmly committed to that part.