Canada may be forced into uncomfortable political territory and compelled to invest in technology that can shoot down cruise missiles as part of the upcoming overhaul of the North American Aerospace Defence Command (Norad), say defence experts.

Renegotiating the North American Free Trade Agreement may suck much of the political oxygen out of Ottawa in the near future, but the modernization of the decades-old Norad relationship is fraught with many expensive pitfalls and trade-offs, particularly with a White House determined to put America first.

The notion of updating Norad was — significantly — an initial point of common ground between Prime Minister Justin Trudeau and U.S. President Donald Trump in their first meeting last February and it was also referenced in the Liberal government's highly promoted defence policy in June.

The implications, however, remain hazy at best.

Part of the reason is that there has been no bilateral consensus on what elements will be overhauled, says defence analyst Andrea Charron, of the University of Manitoba.

Cruise missile consensus

But there is general agreement, at least among U.S. military commanders and security observers, that defending against cruise missiles is an issue of growing importance. They are proliferating at what U.S. officials say is an alarming rate.

"It is time for America to prioritize homeland cruise missile defence," according to retired U.S. brigadier-general Kenneth Todorov who, until 2015, served as deputy director of the U.S. Missile Defence Agency. Todorov's comments were part of a report last spring for the prominent Washington think-tank, the Center for Strategic and International Studies.

Much of the missile defence discussion, including the decades-long politically toxic debate in Canada, has centred on the threat of high-flying intercontinental ballistic missiles.

Deter, detect, defend: Norad is North America's best hope against a Soviet air attack. 3:47

But cruise missiles — which remain powered throughout flight — are slower, fly lower, and are harder to spot and shoot down.

One of the biggest and perhaps most costly elements of the Norad overhaul will be reconditioning the 1980s-vintage North Warning System, a chain of radar stations in Alaska and Northern Canada that has been the primary line of defence against bombers and cruise missiles for decades.

Improvements to the system, which is not intended to track some ballistic missiles, were left outside of the Trudeau government's carefully costed defence spending plans.

There may be good reason for obfuscation.

Political choices

The threat posed by cruise missiles means the Liberal government will face a series of hard political, fiscal and possibly military choices as the modernization unfolds over the next few years.

Regardless of who might do the shooting — Russia, China or even terrorist organizations — U.S. military planners believe there would be little time to react once a missile is inbound. That's why making a pre-emptive strike against the enemy's launch platforms — whether submarines, surface ships or bombers — is the preferred method of dealing with the threat.

But the prospect of such strikes will raise a host of politically uncomfortable problems for the Liberal government as they hammer out the Norad overhaul. Canada has traditionally shied away from pre-emptive attacks and may prefer to leave such missions to U.S. forces, as it has in the past.

Russian Air Force Tupolev Tu-95MS in-flight over Russia. There is growing concern at Norad about the ability of Russian bombers to launch cruise missiles from international airspace. (Ilya Naymushin/Reuters)

"There is going to have to be approval between U.S. and Canada that this is the route to go," said Charron, who co-authored a study on Norad modernization with fellow analyst James Fergusson.

The issue becomes more complicated and dangerous when action has to be taken in international waters or airspace.

"That would require political confirmation and that is potentially a slippery slope we don't want to go down," she said.

That means, in order to cover the huge northern gap, the Liberal government would almost certainly have to allow U.S. fighter jets to use Canadian bases and forward landing strips in the North on a more frequent basis.

Better air defences?

If Canada doesn't participate in pre-emptive strikes, one of the trade-offs would likely be installing anti-cruise missile batteries on our own soil, according to Charron.

Charron says the Canadian military possesses limited, if any, such capabilities.

The navy's recently retired destroyers had advanced SM-2 interceptors, but there is very little in the way of land-based systems in Canada's inventory.

A U.S. Army Avenger battery, belonging to the North Dakota National Guard, fires a test missile during a 2008 exercise in Texas. (U.S. National Guard)

Some anti-cruise missile interceptor technology is still in the development stage and is extraordinarily expensive. But there are proven systems out there.

Charron notes that during last fall's annual Norad exercise — known as Vigilant Shield — the Americans deployed 60 members of a U.S. National Guard unit to Canadian Forces Base North Bay. The troops operated Boeing Avenger surface-to-air missiles, which are intended to shoot down cruise missiles at short range.

If Canada was uninterested, or unable, to invest in systems like that, Washington would likely require under a revised Norad arrangement that even more U.S. personnel and equipment be based on Canadian soil, she said.

The political considerations and financial cost don't end there.

Barrage balloons

The Pentagon has been experimenting with giant aerostats — balloons, tethered to the ground and equipped with sophisticated radar — called Joint Land Attack Cruise Missile Defence Elevated Netted Sensor System (JLENS).

Floating at just over 3,000 metres, they can scan the sky and see moving objects better than ground-based radar.

Documents obtained by CBC News under the Access to Information Act show the Royal Canadian Air Force has been looking at the utility — and the survivability — of aerostats in the harsh Arctic climate.

A file photo of Joint Land Attack Cruise Missile Defence Elevated Netted Sensor System (JLENS) which is designed to detect cruise missiles flying close to the ground. (U.S. Army Handout)

But the U.S. Government Accountability Office has expressed skepticism about JLENS and whether it can be expanded.

The Pentagon has spent $2.7 billion on JLENS and has a series of the helium-filled balloons deployed near Washington, where in 2015 they failed to spot a protester who flew a single-seat, rotary-wing aircraft onto the lawn of the White House.

Norad said the system wasn't operating that day.