CRA disagrees with TD Securities

CRA, in addition to applying  Art. IV(6) of the Canada-U.S. Treaty (added by the 5th Protocol) on the basis that an LLC is only entitled to claim Treaty benefits (e.g., reduced Canadian withholding or branch tax) if the amount in question is considered to be derived by a U.S. resident who qualifies under the limitation-of-benefits Article, also "is not in agreement with the decision in TD Securities," so that it presumably will challenge any pre-Protocol benefits claimed by an LLC.

Neal Armstrong.  Summary of 25 September 2012 B.C. CTF Round Table, Q. 10, 2012-0457591C6 under Treaties - Art. 4.