Canada

This is entirely a non-starter. We simply do not have the technology to intercept ICBMs on anything but a local scale. Guarding thousands of km of our boarder isn't feasible when you have literal seconds to intercept something that could land minutes away. I mean, ICBMs are hypersonic by definition since they fall at a rate of something like mach 20. It's like trying to stop a bullet by throwing a BB at it. It can only work by placing ICBM interceptor sites every hundred KM or something across the entire boarder.

Imagine funding billion dollar interceptor missiles by the thousands. And that presumes that we have ones that work.

The Iron Dome works because it intercepts rockets that are technologically more similar to WWII Soviet weapons than modern day missiles. Against that, an ICBM is like comparing a hobby rocket to SpaceX's Space Ship One.

Any serious talk about it is simply grifting, and Canada shouldn't take part unless if the other side could provide evidence of it working without the projected costs being greater than our entire GDP. And even then, who are we going to use it against? The Russians? All evidence points to them not being able to get their existing ICBMs to work, let alone make new ones. And Canada isn't in between China and the US, so that's not a threat to us at all. And that presumes that China can lob an ICBM at several times the distance Russian needs to.

And all this presumes that we can trust anything that's said regarding any kind of friendly cooperative from the south. First try ending your damn trade war with us, then we can start talking about some smaller low stakes cooperatives before ramping things up to things that has the potential to cripple our entire economy and autonomy.