The cold war experience of tit-for-tat has two lessons:

Firstly, somebody has to make a move either at parity which is respected or below, and the "you blinked first" message has to be ignored.

Secondly, there are always collateral damages. You can't afford to expel Russian diplomatic staff so you expel east Germans. You don't want to risk core staff so you send friendly nations into harm's way.

Canada was thrown into harm's way to avoid a bigger problem. The question is: who is willing to de scale the tit-for-tat response first?