First, some European countries have overseas territories in Latin America, like French Guiana, their zoos can easily acquire species from these territories. By contrast, US has overseas territories in the western Pacific so US zoos have Mariana Doves, Guam Rails and Guam Kingfishers that European zoos probably don't have.
Second, Canadian zoos have relatively poor collections overall, even Giant Anteater and Lowland Tapir are kept by only one institution in Canada. So it is basically US alone vs entire West Europe.