Exhibit 2.43





VIDEOTRON LTD. / VIDÉOTRON LTÉE





FIRST
SUPPLEMENTAL INDENTURE

Dated as of November 4th, 2011





Computershare Trust Company of Canada,

Trustee











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FIRST SUPPLEMENTAL INDENTURE, dated as of November 4th, 2011 (this First Supplemental Indenture), by and
among Videotron Ltd. / Vidéotron Ltée, a corporation under the laws of the Province of Québec (the Corporation), 9253-2233 Québec Inc., a corporation under the laws of the Province of Québec
(2233), 9253-2456 Québec Inc., a corporation under the laws of the Province of Québec (2456 and, together with 2233, the Additional Subsidiary
Guarantors and each an Additional Subsidiary Guarantor) and Computershare Trust Company of Canada, as trustee (the Trustee), to the Indenture (the Indenture),
dated as of July 5, 2011, by and among the Corporation, each of the subsidiary guarantors party thereto (collectively referred to as the Original Subsidiary Guarantors) and the Trustee.

WHEREAS, the Corporation, the Original Subsidiary Guarantors and the Trustee have entered into the Indenture
governing the Corporations 67/8% Senior Notes
due July 15, 2021 (the Notes);

WHEREAS, Section 4.19 of the Indenture provides that
under certain circumstances the Corporation shall cause a Restricted Subsidiary to execute and deliver to the Trustee a supplemental indenture providing for a Subsidiary Guarantee of the payment of the Notes by such Restricted Subsidiary;

WHEREAS, the parties hereto are desirous of further supplementing the Indenture in the manner hereinafter provided for the
purpose of providing Subsidiary Guarantees by each of the Additional Subsidiary Guarantors in accordance with the terms of the Indenture;

WHEREAS, Section 9.01(5) of the Indenture provides that the Corporation and the Trustee may amend or supplement the Indenture without the consent of any Holder to add additional guarantees with
respect to the Notes; and

WHEREAS, all things necessary have been done to make this First Supplemental Indenture a valid
agreement of the Corporation, each of the Additional Subsidiary Guarantors and the Trustee, in accordance with its terms.

NOW, THEREFORE,
THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH:

For and in consideration of the premises contained herein, the parties hereto
mutually covenant and agree as follows:

1. Terms used in this First Supplemental Indenture that are not defined herein shall
have the meanings set forth in the Indenture.

2. Each of the Additional Subsidiary Guarantors hereby agrees to provide an
unconditional Subsidiary Guarantee on the terms and subject to the conditions and limitations set forth in the Indenture, including but not limited to Article 10 of the Indenture.

3. This First Supplemental Indenture shall be construed as supplemental to the Indenture and shall form a part thereof, and the Indenture
is hereby incorporated by reference herein and, as supplemented, modified and restated hereby, is hereby ratified, approved and confirmed.



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4. This First Supplemental Indenture shall be effective as of the date hereof. On and after
the date hereof, each reference in the Indenture to this Indenture, hereunder, hereof, or herein shall mean and be a reference to the Indenture as supplemented by this First Supplemental Indenture
unless the context otherwise requires.

5. Except as provided below, in the event of a conflict between the terms and
conditions of the Indenture and the terms and conditions of this First Supplemental Indenture, the terms and conditions of this First Supplemental Indenture shall prevail.

6. If any provision of this First Supplemental Indenture limits, qualifies or conflicts with another provision of the Indenture that is required to be included by the Trust Indenture Act of 1939, as
amended (the Act), as in force at the date this First Supplemental Indenture is executed, the provision required by said Act shall control.

7. This First Supplemental Indenture shall be governed and construed in accordance with the laws of the Province of Quebec and the federal laws of Canada applicable therein. The parties hereby acknowledge
that they have expressly required this First Supplemental Indenture be drawn up in the English language only. Les parties reconnaissent avoir expressément demandé que la présente convention soit rédigé en
anglais seulement.

8. This First Supplemental Indenture may be signed in any number of counterparts with the same effect
as if the signatures to each counterpart were upon a single instrument, and all such counterparts together shall be deemed an original of this First Supplemental Indenture.

9. The recitals contained in this First Supplemental Indenture shall be taken as the statements of the Corporation, and the Trustee assumes no responsibility for their correctness. The Trustee makes no
representations as to the validity or sufficiency of this First Supplemental Indenture.

[SIGNATURES ON FOLLOWING PAGES]



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IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental Indenture to be
duly executed as of the day and year first above written.



|                                      |  |                                                        |  |  |  |     |  |                                                               
|------------------------------------- |  | ------------------------------------------------------ |  |  |  | --- |  | --------------------------------------------------------------
|CORPORATION:                          |  |                                                        |  |  |  |    
|                                      |  |                                                        | 
|VIDÉOTRON LTÉE                        |  |                                                        |  |  |  |    
|                                      |  |                                                        |  | 
|By:                                   |  | /s/ Chloé Poirier                                      |  |  |  | By: |  | /s/ Christian Marcoux                                         
|                                      |  | Name: Chloé Poirier                                    |  |  |  |     |  | Name: Christian Marcoux                                       
|                                      |  | Title: Treasurer                                       |  |  |  |     |  | Title: Assistant Secretary                                    
|                                      |  |                                                        | 
|ADDITIONAL SUBSIDIARY GUARANTOR:      |  |                                                        |  |  |  |    
|                                      |  |                                                        | 
|9253-2233 QUÉBEC INC.                 |  |                                                        |  |  |  |    
|                                      |  |                                                        |  | 
|By:                                   |  | /s/ Chloé Poirier                                      |  |  |  | By: |  | /s/ Christian Marcoux                                         
|                                      |  | Name: Chloé Poirier                                    |  |  |  |     |  | Name: Christian Marcoux                                       
|                                      |  | Title: Treasurer                                       |  |  |  |     |  | Title: Assistant Secretary                                    
|                                      |  |                                                        | 
|ADDITIONAL SUBSIDIARY GUARANTOR:      |  |                                                        |  |  |  |    
|                                      |  |                                                        | 
|9253-2456 QUÉBEC INC.                 |  |                                                        |  |  |  |    
|                                      |  |                                                        |  | 
|By:                                   |  | /s/ Chloé Poirier                                      |  |  |  | By: |  | /s/ Christian Marcoux                                         
|                                      |  | Name: Chloé Poirier                                    |  |  |  |     |  | Name: Christian Marcoux                                       
|                                      |  | Title: Treasurer                                       |  |  |  |     |  | Title: Assistant Secretary                                    
|                                      |  |                                                        | 
|TRUSTEE:                              |  |                                                        |  |  |  |    
|                                      |  |                                                        | 
|COMPUTERSHARE TRUST COMPANY OF CANADA |  |                                                        |  |  |  |    
|                                      |  |                                                        |  | 
|By:                                   |  | /s/ Fabienne Pinatel                                   |  |  |  | By: |  | /s/ Pierre Lavoie                                             
|                                      |  | Name: Fabienne Pinatel                                 |  |  |  |     |  | Name: Pierre Lavoie                                           
|                                      |  | Title: Gestionnaire fiduciare /Corporate Trust Officer |  |  |  |     |  | Title: Gestionnaire fiduciare adjoint /Associate Trust Officer

First Supplemental Indenture to 2011 Indenture