A one time $100,000 payment to every Canadian citizen would cost $3.5 trillion. Which is only 3 years of the budget deficit and 1/3 of the federal debt. And could easily be borrowed at the record low interest rates the US government has access to.
Yet $100,000 is an offer the vast majority of Canadians could not refuse. And for a thing, joining the US, that many would agree to for free, recognizing it as an improvement. Freedom of movement between the two countries for example, would see millions of Canadians moving south.
At negative real borrowing rates, the investment is easily profitable even if Canada didn't have vast natural resources, resources that solve many of America's problems. It would also serve as massive, yet profitable, stimulus spending.