Exhibit 5.3

	Mayer Brown LLP 71 South Wacker Drive Chicago, Illinois 60606-4637
	Main Tel +1 312 782 0600
December 23, 2019	Main Fax +1 312 701 7711
	www.mayerbrown.com

TransCanada PipeLines Limited

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. 333-235546) of TransCanada PipeLines Limited.

Very truly yours,

/s/ Mayer Brown LLP

Mayer Brown LLP

Mayer Brown is a global services provider comprising an association of legal practices that are separate entities including
Mayer Brown LLP (Illinois, USA), Mayer Brown International LLP (England), Mayer Brown (a Hong Kong partnership)

and Tauil & Chequer Advogados (a Brazilian partnership).