I don't think that basis for the agreement is grounded in reality at all between the United States and Canada. People who can't get protection in the United States because it has not been a safe third country for them have been coming to Canada. Canada has never had an overwhelmingly large number of refugees from the United States at its borders.
It has been an important refuge for persons from the United States who have not been able to get protection there. It was a critical safety valve for Central Americans. It was a critical safety valve for Colombians.
Generally, around the world, I think the reason we are having safe third country agreements, the reason countries are entering into them, is because they are disrespecting their obligations under the 1951 convention.
The worldwide trends are that the numbers of refugee applications that are coming to the countries of the north have gone dramatically down. The UNHCR is very concerned about this. And the vast majority of refugees remain in the developing world.
So, no, I don't think the reason for this is forum shopping.