LPT here:

In an airport like Halifax, there are supervisors on-duty, as well as the port director. If for any reason you feel as if you are not being treated fairly or legally, demand to speak to the person in charge and make your case known.

If you are at a smaller port and there's no one on duty, withdraw your request to enter the country and return. You want a turnaround.

I've often seen it happen when people from Vermont miss an exit or a road and turn into a border station with a gun. You just withdraw and go back and it's fine, but it's otherwise illegal. Since you're not entering Canada and leaving, there's no crime.

On the US side it's a bit trickier because they can detain you and seize your data much easier. But again, it's CBP policy for you to have a supervisor if you want one. If something like this is happening to you, get a supervisor.

Here's the common theme with both sides: the officer needs to fill out a report. You want to ensure it's done truthfully, because if you end up in court (and I'm not talking you suing, I'm talking you being prosecuted), you want a supervisor there to testify as well.

As a matter of procedure, supervisors with CBP can go against what the agents want or do. Thus, if you found yourself in a situation where an agent was determined to look at your phone, you have a chance that a supervisor would overrule them.

With CBSA it's a bit different. Do not fuck up with them because as a matter of policy they aren't to go back on any action taken. If they say they're going to do "x", then they can't go back and do something lesser. For the most part, management will back up the officer and not overrule them. The reason you want to speak to a supervisor is when you make a complaint to Ottawa, because they have to be neutral (and are).

In the USA, their policies and laws are broad and vague and can basically do whatever they like. But if you look like you know your rights and will be problematic, you stand a better chance of negotiation rather than retaliation.

In Canada, it's the exact opposite. The harder you push, the worse the penalties will escalate for you, which is why you always want to try and withdraw and go back from whence you came. The supervisor or management will likely not help you or overrule anyone, but they will be fair and impartial if you have a valid complaint in the future.

Finally, I'll leave you with this tidbit: a person I know who works for CBSA deletes all of their text messages and disconnects their email accounts when crossing the border. That alone should tell you all you need to know.