T2125 only applies to proprietorships or partnerships, not corporations.
This is a very technical question in Canada as we do not have LLC's. We might have Limited Liability Partnerships, which may be different from province to province, and are usually limited to doctors and lawyers, etc. Generally LLC's are considered to be corporations, which might mean that the revenue and expense of the LLC could not be filed as a partnership in Canada. The only way to get a definitive answer for your partner is for him or her to talk to an
accountant in Canada as to how to file, or if there is any benefit to filing.
