Think he might have received a call from several utility & regulatory entities telling him that we have an interconnected grid that already has several rules in place for import & export. NERC oversees the grid for the US, Canada & Northern Mexico due to the interconnected relationship of these 3 grids (eastern, western & Texas). Ontario is also heavy in nuclear as well as hydro generation. Without the ability to produce hydro power, they will be more limited in the ability to move water or provide payback for their heavy nuclear investments lately. With their heavy usage of DC transmission, they would also require heavy investment into additional DC/AC stations to provide usable distribution instead of relying on neighboring Provences & the US to supply frequency stable AC to their load centers.
The North American BES is the largest & most complex machine ever built by man. You can’t just cut off a hand and expect to retain full usage of the arm.