If you are just selling into the US into other states then it is OK to do so from your incorporated office. If you want to setup a shop eg hire employees etc then you have to have a special foreign state license in each of the states . I think it is the same in Canada. The company I mentioned is mainly for business formation, however, they will help inobtaining non-US citizen tax numbers/social insurance number/filing paperwork for setting up business/office in different states. On the other issues, like visas, it may be wise to contact US lawyers that specialize in this field.