I haven't heard of it. Please quote your source of information about what you heard. Let's share.
My gut feeling is US, as the No.1 strongest nation in the world, will do whatever it can to pressue Canada to offer US nationals the convenience of travel.
There have been cases where US passport holders can enter a country (e.g. Thailand, Taiwan) visa-free for tourism while citizens from these countries need to obtain US visas to visit the US.