The Pinetree Radar array was on Canadian soil, manned by thousands of Canadian and American Armed Forces personnel throughout the cold war from the 1950's to the 1990's. In addition, the Distant Early Warning (DEW) line was constructed even further north for interception of nuclear missiles and enemy aircraft flying over the north, northwest, and northeast polar regions.

Here are some excerpts from a 1954 Canadian Gov't briefing on Canada-US relations on Continental Defence:

...
(c) There was increasing pressure in the United States, particularly from certain Congressional quarters, to speed up the preparations for continental defence. If Canada indicated now that it would construct the line running along the 55th parallel, accusations could not be made that we were not doing our share in protecting the continent. If we held up on the mid-continent line, we might find ourselves engaged eventually in a joint operation with the United States at a greater cost and with less control than we otherwise would have had. There would also be the added delays involved in consultation over the type of equipment to be used, plans, specifications, and the like. On the other hand, if it were to be a Canadian project, the U.S. authorities should be kept fully informed of the technical details and of the construction processes, in order to ensure that the early warning line met the operational requirements of both U.S. and Canadian Air Forces.
...
(i) If Canada accepted full responsibility for the construction and the cost of the mid-continent line, it might be found that all available resources were committed, with nothing left over for use on the far northern line if it were to be built. At that point, pressure from the United States might be so great that we could not resist allowing them to construct it alone. The political consequences, if this were the case, would be most undesirable.

(j) Even if Canada built the mid-continent line alone, efforts should be made to agree on division of costs and work on the DEW line as was done in the "Pinetree" operation. Present American thinking envisaged it being constructed in one season as a task force operation and, regardless of how the cost might ultimately be shared, it seemed quite likely that the United States would have to play a major part in the transportation of the necessary equipment, simply because Canada did not have enough ships or aircraft. For the same reason, the United States would have a significant role to play in the supply and maintenance of the line. Some estimates of cost had been given for the project but these appeared to be quite inaccurate and it was not possible at this stage to say what amount of money would be involved.

(k) The U.S. Chiefs of Staff had been informed that the Canadian Chiefs of Staff would let them know by the end of June whether Canada would construct the mid-continent line alone, or whether other arrangements should be made.

4. The Committee, after further discussion:

(a) agreed to recommend that an aircraft warning line in the vicinity of the 55th parallel of latitude from Hopedale in Labrador to the mountains on the B.C.-Alberta border be constructed by Canada at a cost estimated to be of the order of $120 million, the money to be provided from current appropriations for the Department of National Defence and the appropriations now contemplated for the next few years; it being understood that the construction of the section of the line from the B.C.-Alberta border to the Pacific Ocean would be considered at a later meeting following further studies;

(b) noted that a proposal to construct a distant early warning line running along the northern coast of the continent would likely be made in the near future and that it would be desirable that this line be built as a joint Canada-United States project;

(c) agreed that once the final decision had been taken by the Cabinet with respect to (a) above, the Permanent Joint Board on Defence should be so informed.

------------------------------------------------------------------------------

27 Approuvé par le Cabinet le 30 juin 1954.
Approved by Cabinet, June 30, 1954.

========================================
========================================

Canada has done plenty to defend North America.