Indeed, sections 25.1 to 25.4 have no effect on matters relating to evidence. They stay the same, whether we discuss section 25.1 or not.
On the other hand, if I were a defence lawyer and my client had been accused of an offence under the Criminal Code or the criminal law, and I knew that the police used these sections, the question would be why the police officer believed the act to be reasonable and proportional. The issue then would be the police officer's credibility, perhaps three or four years after he had committed the act in question, because these undercover operations can take a long time. You can spend a lot of time collecting the evidence you need where organized crime is concerned. That police officer would testify before a judge and his credibility could be questioned, because the events had taken place three or four years earlier.
However, if the police officer had prior written authorization, that would constitute evidence. The Crown prosecutor could then say that he was allowed to commit this act because it been authorized by a senior official or by a judge.
If I were a criminal lawyer and had to defend a client, I would really like these sections, either way. Once the trial was underway, I could say that these sections pose major problems and do not adequately limit police powers. I would attack the credibility of the police officer who committed the act under these sections -- in other words, the very constitutionality of the regime. I would say there are so few conditions laid out in these sections that just about anything goes, and that that is unconstitutional.
I believe that for the proper conduct of operations carried out under these sections, Parliament should consider limiting the scope of the law to avoid the kind of attack that a defence lawyer could mount under the current regime.