If some banks don't comply, then under FATCA, they would be non-participating financial institutions, and there would be a 30% withholding tax on them. And that's a withholding tax and not a withholding-against tax. It is a tax. You don't get it back.
Under the IGA, Canadian financial institutions only slip into that non-participating classification after 18 months of continuous notification by CRA that they're not compliant, and they need to get compliant. So there's a very big window to get things in order.