You can choose Flat Rate or Calculated for domestic (Canada) shipping.
You can choose Flat Rate or Calculated for international shipping, which includes the USA which is a foreign country.
This is not a change, it's been like that for years.
When you set up international shipping, first choose Custom Location
then choose USA and set up your shipping service.
Then choose Offer Additional Service and choose Custom Location again and choose the other countries you want to ship to.
Do NOT choose N&S America or USA in this second section, as it will override the original USA rates.