In fact, the Canadian federal mandate does not prevent the unvaccinated truckers (and other Canadians) from going to the USA. It’s the American mandate that’s doing that.
The Canadian mandate prevents unvaccinated truckers from coming into Canada.
Which is to say, it’s preventing unvaccinated Americans from coming in, because there aren’t any unvaccinated Canadians allowed into the US from which to return.
And even if an unvaccinated Canadian trucker were to somehow get into the US, they’d still be allowed back, because the government can’t prevent a Canadian from returning home.
The Canadian mandate prevents unvaccinated truckers from coming into Canada.
Which is to say, it’s preventing unvaccinated Americans from coming in, because there aren’t any unvaccinated Canadians allowed into the US from which to return.
And even if an unvaccinated Canadian trucker were to somehow get into the US, they’d still be allowed back, because the government can’t prevent a Canadian from returning home.