CRA indicates that trailer fees are GST/HST exempt only if the dealer is not providing on-going client services in order to earn the fees

CRA has ruled that trailer fees received by dealers from the investment manager for an investment fund (presumably, a mutual fund) will be considered to be exempt consideration for having facilitated the sale of shares in the fund only if the dealer does not provide any post-sale servicing of the investor's account in order to earn the trailer fees, e.g., regularly contacting the client to review the appropriateness of this investment, and reviewing alternatives.  Although this may sound like a statement that trailer fees are exempt only if the investment dealer is not doing a good job, in fact this statement may not be problematic as the trailer fees will be earned by the dealer based on the level of continued investment in the fund irrespective of the level of post-sale service provided by the dealer.

Neal Armstrong.  Summary of 15 March 2012 Ruling 132880-2 under ETA s. 123(1) - financial service.