If you mention “the constitution” you are probably referring to another country.
In Canada, this would be a charter issue, but it’s not a charter issue.
A requirement of driving is having BAC below 0.8.
This is a traffic stop, where the point is to confirm that there are not legal issues with the vehicle or its operation. The search of showing your license is already more of a privacy issue than providing a breath sample.
If you’re more curious about it, read section 8 of the charter.