In the 3 banks I've worked with in Canada, all were completely unable to access my American credit history.
The governments do share tax data, but AFAIK the banks have no way to link "John Smith SSN:123-45-6789" to "John Smith SIN:098-76-54321". They even have my US SSN number since Canadian banks report to the IRS.
Edit: here's experian explaining it: https://www.experian.com/blogs/ask-experian/u-s-credit-histo...