In order to have safe third country agreements you need to have a standard for everybody, and the standard has to be respected, implemented, and enforced. In reality, right now each country decides on the definition and the procedure on detention, removals, and everything, and it's very difficult to compare. You are forced to compare your system to other systems.
The criteria used to define a safe third country are not fundamentally right. It is a country that has signed the refugee convention and has a process for refugees—there is this and there is that. So in a very superficial manner, every single country on earth could be a safe third country for refugees, but in a practical manner we know that every national reality has very clear implications.
Let me give you an example that in our reality would be totally unacceptable. A Cuban touches the shores of the United States and is accepted and protected. In Canada that would be totally against our law, because we don't have that kind of privilege for particular groups of people coming in. In that way there would be mandatory detention, and different things would happen. Issues like violation of international law, etc., would mean that comparing this to countries in a very superficial way wouldn't define a safe third country in reality.