I used to work for a US company as a remote employee (contractor). I'm a canadian citizen, so it will be different if you dont have the right to work here, but for me its pretty easy. You're basically considered self-employeed and have to declare your income. You also have to register for a GST number (you don't have to charge gst, but you do have to report charging $0. Its weird). The tax forms are easy enough you can definitely just print them out and fill out yourself, or hire a tax person to do them for you. (Disclaimer: not an accountant, hire a real one if you want real tax advice).

I have no idea how it works if your not a citizen. In general i think work visas are fairly easy to get if you are a skilled worker like a software engineer, especially coming from a NAFTA country.