It depends on how pedantic we want to get.

Technically, Canada was a vassal of the UK until fairly recently. The laws dismantling that technicality started in 1926 and were mostly finalized in 1982. They still have an odd vestige of that where the Canadia monarch is defined as whoever happens to be the British monarch at the time.

For all practical purposes, the Brits haven't held sovereignty over Canada in ages.

While the US was never officially Canada's suzerain, the vast differences in economies, militaries, and populations mean that diplomatic and trade negotiations are tilted in the favor of the US.

The whole advantage of soft power over hard power is that it enforces vassalage without looking like it's enforcing vassalage.