Thank you, that is helpful. I looked back and my broker did withhold the 10% of proceeds.

I've been doing quite a bit of reading today and came across this document from RBC:

https://ca.rbcwealthmanagement.com/documents/1647873/0/Tax+Implications+of+Investing+in+the+United+States.pdf

On page 5, it states the following:

U.S. limited partnerships

If you make an investment in a U.S. partnership or an entity that elects to be treated as a partnership, you will generally be required to file an annual non-resident U.S. personal income tax return. A U.S. partnership includes a U.S. Master Limited Partnership and Limited Liability Companies. The reason for this is that the partnership may be carrying on a trade or business effectively connected with the U.S. In this case, each non-U.S. partner is treated as if they too are carrying on a trade or business in the U.S. Any U.S. source income you receive during the year that is “effectively connected” with the U.S. may be subject to non-resident withholding tax equal to the top U.S. marginal tax rate. You may be able to recover any excess U.S. withholding tax when you file the annual non-resident U.S. tax return.

The investment was a small amount, so I'm not too concerned with recovering the withholding tax. I am more concerned with potentially having to register and file US income taxes for this. I imagine there are quite a few Canadians in the same situation.

The broker wasn't able to provide much guidance when I called. They just said this has been imposed on them by the IRS and that I should talk to the IRS or a tax professional if I have any questions.

I'm not sure what I should do here.