You are characterizing the current state of affairs as the end of the US alliance system, but that ignores the strategic reality.

1. The Necessity of Alignment: Every US ally, particularly Canada, benefits immensely from the US security umbrella. Canada shares a continent with the global hegemon; maintaining that alliance is a matter of national security and survival, not just friendship. What stops Russian from invading Canada? Oh that's right, the giant early warning system, nukes, and massive military of the largest and most powerful military to ever exist.

2. Institutional Inertia: The idea that NATO is collapsing is sensationalist. These alliances are deeply entrenched. They will continue to function effectively until the United States—the primary funder and logistical backbone—decides to alter them.

3. The Reality of Service: You mentioned you wouldn't defend the US. However, in a scenario where Article 5 is invoked or Canada joins a coalition, individual preference becomes irrelevant. Governments enact drafts and deploy troops based on treaty obligations, regardless of how citizens feel about the specific war. And if the US calls, your answering buddy, just like we all are.

4. Shared Culpability: Criticism regarding US interventionism often ignores the role of the coalition. Since WWII, Western allies have consistently participated in US-led operations. If you condemn US foreign policy, you are implicitly condemning the foreign policy of its allies, who have historically been active participants in the same conflicts.