As a 'work in progress' I am researching this very subject.

I can tell you that in March 1942, the RN had 67 vessels, the RCN 61 vessels, and the USN 15 destroyers and some Coast Cuard cutters.

By April 1942, the USN destroyers were gone and only the cutters remained. The latter stayed throughout the war heading up American escort groups (e.g. A-1) whose principal members were British and Canadian corvettes.

Later in the war, USN DDs provided close escort for Troop convoys but not for the regular fast and slow convoys carrying food, oil and war materiel.

There were also Free French and Norwegian vessels acting as close convoy escorts mixed in with British and Canadian groups. And there may have been Belgian, Polish and Danish naval vessels on the eastern end as well.

The USN returned to the Atlantic in force in early spring 1943 but again only with "hunter-killer" carrier groups, not close convoy escorts.

But you have to read a lot of specialty books to locate this information. If you visit the USN Museum in Norfok, VA, for example, you can easily gain the impression that the USN fought and won the Battle of the Atlantic all by itself.

Basically, by 1944 the RCN provided almost 50% of the close convoy escorts, the rest being British, Norwegian, Free French, etc. But I have no stats yet to back this up.