Ferrari has opted not to add a fourth turbo element to Charles Leclerc's pool of hardware, thus preserving the Monegasque, for now, from a grid drop in Montreal.
Leclerc's engine failure in Baku resulted in the Italian outfit introducing a fresh ICE, MGU-H and MGU-K into the Monegasque's power unit inventory.
The additions are penalty free, but the Scuderia is still pondering where and when to add a fourth turbo, which means that a grid drop will sooner or later hit Leclerc.
However, over at AlphaTauri, the Faenza-based outfit has fitted Yuki Tsunoda's AT03 with an entirely new power unit, a choice justified by the raft of engine issues encountered by the Japanese driver since the start of the season.
Consequently, Tsundoa will start his Canadian Grand prix on Sunday from the back of the grid.
Among the other PU changes in the field, Alpine has added a fresh ICE, turbo, MGU-H and MGU-K to Esteban Ocon's collection of hardware.
They are also the final elements for which the Frenchman will dodge a grid penalty.
Finally, Haas has added a fresh ICE, turbo and MGU-H to Kevin Magnussen's elements as a result of his Ferrari engine issues in Baku.
The Dane also gets a free pass for this weekend, but will incur a grid drop upon the next changes.