To the best of my knowledge, those DEW radars were for air defense, not missile defense. If they're planning on upgrading them for the ballistic missile warning mission, it'd require a substancial change in the equipment.

Perhaps they're to be upgraded at part of the LAATD (Low Altitude Air Threat Defense) effort. That effort is looking to detect and destroy cruise missiles instead of ballistic missiles. Canada is an active partner in LAATD with NORAD. I've sat in on some of the meetings.

Detecting, tracking, and engaging low altitude air threats, especially fast moving ones like cruise missiles, is a huge challenge. They need all of the radar coverage they can get. One technology they're exploring is very high altitude unmanned blimps that could stay up for weeks or months at a time and serve as radar platforms. From those altitudes, a radar could see for a radius of several hundred miles.