Generally speaking, you can't be a resident of two countries that have a tax treaty at the same time. Specifically in this case, US and Canada.
You need to determine if they are a resident of the US or Canada before you can fill out this section.
They may of course still have to file a return in the US and be taxed on their worldwide income if they are either a US citizen, Green Card holder, meet the substantial presence test, etc. However, if they are considered residents of Canada, they are NOT residents of the US at the same time.
If they are considered residents of both countries, Article IV (treaty tie breaker rules) must be used to determine which country they are a resident of.
Factors considered include where they own a home, where their spouse and dependants live, where they live most of the time, where they work, where their social ties are, etc.
People come to ProFile for help and answers—we want to let them know that we're here to listen and share our knowledge. We do that with the style and format of our responses. Here are five guidelines:
Keep it conversational. When answering questions, write like you speak. Imagine you're explaining something to a trusted friend, using simple, everyday language. Avoid jargon and technical terms when possible. When no other word will do, explain technical terms in plain English.
Be clear and state the answer right up front. Ask yourself what specific information the person really needs and then provide it. Stick to the topic and avoid unnecessary details. Break information down into a numbered or bulleted list and highlight the most important details in bold.
Be concise. Aim for no more than two short sentences in a paragraph, and try to keep paragraphs to two lines. A wall of text can look intimidating and many won't read it, so break it up. It's okay to link to other resources for more details, but avoid giving answers that contain little more than a link.
Be a good listener. When people post very general questions, take a second to try to understand what they're really looking for. Then, provide a response that guides them to the best possible outcome.
Be encouraging and positive. Look for ways to eliminate uncertainty by anticipating people's concerns. Make it apparent that we really like helping them achieve positive outcomes.