It's not about any mandate, because there isn't one. If people don't want to get vaccinated they can quarantine for 14 days when they cross the US-Canada border. Or they can just move trucks domestically within Canada or the US. All those options are open to them. Truckers just no longer get a special cross-border exemption and have to play by the same rules everyone else has for a while when they cross the border (vaccinated or quarantine)