The first flights back in the air were domestic diversion recovery flights by US Part 121 operators. This was followed by international diversion recovery flights by US operators from Canada ONLY, intra-US diversion recovery flights by non-US operators, diversion recovery from Canada ONLY by non-US carriers and finally diversion recovery by US operators from outside Canada. Non-US carriers were NEVER PERMITTED to complete diversion recovery flights that were diverted to places other than Canada. One-time ferry permits were issued to ferry aircraft out of the United States (eg. SAA 747), but no revenue traffic was carried.
"The A340-300 may boast a long range, but the A340 is underpowered" -- Robert Milton, CEO - Air Canada