To clarify, they are talking about foreign direct investment, like Canadian billionaires buying stocks in US companies, which the fed does not directly control, but can incentivize through trade agreements. The US can change their taxes on foreign investment on their side. From the other side, FDI is a reflection of how many shares of US companies are being bought up by non-US investors. The Canadian government does not own foreign stock afaik.

Part of the mind boggling numbers is due to massive inflation of certain US stock valuations in the last few years and related reinvestment of capital gains. For example, if I had $1000 invested in Intel last year after it crashed, it would be worth $2000 now. If I sold that and bought $2000 worth of Nvidia stock, that would count as $1000 net increase in my foreign direct investment, even though I haven't moved any "new" money into the US. Did Intel suddenly double in its assets or revenue? Hell no, it's a lot of speculation. People are gambling in the US market or seeking to influence US companies for economic advantage.