NATO Does Not Apply in the Arctic Ocean

The Arctic Ocean isn't covered by the North Atlantic Treaty. Canada could bomb any foreign subs in the Arctic Ocean and not worry about retaliation from NATO members, including the nation of the sub we bombed (assuming all our ships are safe in the Atlantic, where they belong).

The North
Atlantic
Treaty

Article 5
The Parties agree that an armed attack against one or more of
them in
Europe or North America shall be considered an attack against them all
and
consequently they agree that, if such an armed attack occurs, each of them,
in exercise of the right of individual or collective self-defence recognised
by Article 51
of the
Charter of the United Nations, will assist the Party or
Parties so attacked
by taking forthwith, individually and in concert with
the other Parties, such
action as it deems necessary, including the use of
armed force, to restore and
maintain the security of the North Atlantic
area.
Any such armed attack and
all measures taken as a result thereof
shall immediately be reported to the
Security Council. Such measures shall
be terminated when the Security Council
has taken the measures necessary to
restore and maintain international peace and
security .

Article 6 (1)
For the purpose of Article 5, an armed attack on
one or more of
the Parties is deemed to include an armed attack:
on the
territory of any of
the Parties in Europe or North America, on the Algerian
Departments of France
(2),
on the territory of or on the Islands under the
jurisdiction of any of the
Parties in the North Atlantic area north of the
Tropic of Cancer;
on the
forces, vessels, or aircraft of any of the
Parties, when in or over these
territories or any other area in Europe in
which occupation forces of any of the
Parties were stationed on the date
when the Treaty entered into force or the
Mediterranean Sea or the North
Atlantic area north of the Tropic of Cancer.

List of NATO members.