Canadian Online Business Selling to the States

I'm working with someone to put a business online.  Currently, this person does onsite training to water works operators certified by a professional organization to grant continuing education units needed by all water works operators to maintain their licenses.

Once online and certified, we will be providing this service specifically to the united states at first, because of the growing need for such service and the large marketplace.

The parent company is incorporated and this online company will be a division of the company.  The online company will sell only the service, I.E. you can pay your fee, login to the site, take your course and a fully digital certificate of completion will be issued to prove to the regulatory authority you indeed earned said continuing education credits.

I have the following questions, and if anyone can point me in the right direction I would be very appreciative.

1) Are there any legal issues in selling the online services in the united states? Registration with the federal or local governments, etc?

2) I plan to spend some time in the states after it launches to provide a united states P.O. box for ease of mailing any documents that need to be mailed, as well as promote discounted training bulk packages to utilities.  Do I need a work visa? Are there federal and state registration forms I would need?  What would be my income tax requirements if the parent company from Canada was paying my salary?

I do not have a background in business and would appreciate being pointed in the right direction.

Best regards,

Mike