Can a foreigner work as 1099 contractor?

Answer 1

Be very careful. Different visas are for different employment situations.

In my case under a NAFTA TN1 I can only work W2. Now a lot of employers will still offer 1099 contracts

A lot of agencies will try and push W2 employment because there's a precedent that if you dont pay the self-employment tax (heaver Social Security) the IRS can come after the agency for the money.