What is the worst possible thing Canada do to hurt the US? What if Canada drops the US dollar as reserve currency?

If Canada drops the USD as reserve currency publicly citing that it no longer is a stable currency and switches to the reserve currency to the Euro or Pound or work with BRICS and G5 to create a new global dollar that tanks the US dollar.

Would that be possible and would the US feel the pain of a G7 country abandoning the Dollar for its instability?

Edit: All under peace and non-violence. Just economically.