First I would llike to know who understand the situation here....
There are two airplanes and one controller.
The two airplanes are sequeced for landing, in other situations they would have been assigned with No.1 clearance for landing and No.2.
Both airplanes were to descent, but the No.2 descended 60 Knots faster than the No.1 and overtook the No.1 airplane.
In the normal world they would continue towards the runway and then there is the controller.
The No.2 would then be instructed to go around if the No.1 gets to close behind the No.2 and still lands first (hence the controller said the 737 was doing 170 knots and the No.2 was doing 240 knots).
So here's a sequence problem, are they going to swap the numbers or following the procedures?
An approach controller will sequence IFR traffic to their destination airport runway, not the tower. Towers at busy terminal areas are mainly there to ensure the runways are clear and traffic is moving along efficiently. They do not have a sequencing function when there is an approach controller working the airspace around them.
The whole reason the approach controller was slowing Air Canada down was to prevent a situation whereby it would overtake and thus cause a loss of separation between itself and the traffic it was following. That is the inherent duty of the approach controller here, and Air Canada didn't seem to understand that.