Actually, users of CBSA services do have the ability and right to provide feedback. Don't they have comment cards readily available like they do at Service Canada Centres?

One could view an electronic thing at the booth as a simple mechanism to do so. It gives police ID number -- which is no different than you wearing your badge visibly and/or even looking at the number on your stamp. Either way, you're identifiable/can be found. And pushing a button is definitely a good immediate way of getting feedback and users who have further issues with the officer can fill in a comment card.

So I don't think your union would be against it.

And if it was, then I would suggest that you need to find new leadership or a new union altogether.