Madibo, who had initially been given a yellow card for the tackle, was sent off after it was upgraded to red following a VAR review — the second Qatari dismissal after Homam el-Amin was given his marching orders in the first half.
With Qatar down to nine men, Canada took full advantage to score three more goals.
Saliba — who had replaced the injured Kone — curled in a free-kick to make it 4-0 in the 64th minute.
The substitute celebrated his goal by racing to the sideline to hold up a replica of the stricken Kone’s Canadian jersey.
Another substitute, Jacob Shaffelburg, then helped make it 5-0, his fierce shot turned into the Qatar goal by defender Mohammad Manai.
David, who had scored twice in the first half after Cyle Larin’s 16th-minute opener, then completed his hat-trick in the second minute of stoppage time to complete the rout.
