This is our main tax information forum which deals with topics concerning Canadians living and working in the U.S., U.S. citizens contemplating working in Canada, and all aspects of Canadian and U.S. income tax and related adminstrative issues.
I typically don't check any box. I write the treaty provison, and then write a descrtiption of what I'm doing.
After 20 years, I am severely cutting back on responses. Do not ask specifically for my help. There are a few others on this board that can answer most questions. All the best