<Page>
                                                                    EXHIBIT 12.3

                                 VIDEOTRON LTEE
            COMPUTATION OF RATIO OF EBITDA TO CASH INTEREST EXPENSE
   (DOLLARS IN MILLIONS, EXCEPT FOR RATIO OF EBITDA TO CASH INTEREST EXPENSE)

<Table>
<Caption>
                                                                     YEAR ENDED                 SIX MONTHS
                                                                    DECEMBER 31,              ENDED JUNE 30,
                                                           ------------------------------   -------------------
                                                             2002       2003       2004       2004       2005
                                                           --------   --------   --------   --------   --------
                                                                                        
CANADIAN GAAP
EBITDA(1)................................................   $210.4     $277.7     $341.1     $163.7     $187.5
Cash interest expense(2).................................     76.4       65.1       59.4       30.2       30.1
                                                            ------     ------     ------     ------     ------
Ratio of EBITDA to cash interest expense.................      2.8        4.3        5.7        5.4        6.2
                                                            ------     ------     ------     ------     ------
</Table>

- ---------

(1) As defined and calculated in note 7 to "Selected Consolidated Financial and
    Operating Data."

(2) As defined and calculated in note 9 to "Selected Consolidated Financial and
    Operating Data."