Exhibit 5.4

	Mayer Brown LLP
	71 South Wacker Drive
	Chicago, Illinois 60606-4637
	Main Tel (312) 782-0600
August 5, 2016	Main Fax (312) 701-7711
	www.mayerbrown.com

TransCanada PipeLines Limited

TransCanada Trust

450 - 1st Street S.W.

Calgary, Alberta, Canada, T2P 5H1

Ladies and Gentlemen:

We hereby consent to the references to this firm under the caption “Legal Matters” in the prospectus included as part of the registration statement on Form F-10 ( Registration No. 333-212720) of TransCanada PipeLines Limited and TransCanada Trust.

Very truly yours,

/s/ Mayer Brown LLP

Mayer Brown LLP

Mayer Brown LLP operates in combination with other Mayer Brown entities (the "Mayer Brown Practices"), which have offices in North America, Europe and Asia and are associated with Tauil & Chequer Advogados, a Brazilian law partnership.