You don't have a right to cross a border and spread a deadly disease. As far as I'm aware, these truckers are allowed to work unvaccinated within their own country.
Various disease, actually. Not the flu, but most borders will ask that you're vaccinated for a whole host of diseases if you come for professional reasons.
As far as I understand, Canadians were exempted from these vaccinations for non-covid diseases. That is probably because vaccinations are mandatory as a child in Canada.