Trying to identify this bush. Grow in full sun, dry, clay/sandy soil. I am in Gravenhurst, ON (zone 4). Thank you.
Although it is not possible to say with complete certainty from your photograph, this bush is very likely the bird cherry, or pin cherry, Prunus pensylvanica, which is native to North America and grows in all parts of Ontario except the very far north. It prefers full sun. In Ontario this shrub is often known by both of these common names, although it is worth noting that there is another European bird cherry, Prunus padus, that is native to northern Europe and is closely related to our native chokecherry (Prunus virginiana). Prunus padus and Prunus virginiana are distinguished by their flower clusters which are distinct pendulous racemes – long, oval shaped, drooping clusters. The pin cherry’s flowers, in contrast, grow in the kind of clusters pictured in your image. The small fruit of the pin cherry is bright red and very sour. Here is a website that describes this shrub’s characteristics: https://www.ontario.ca/page/pin-cherry .
For comparative purposes, this website offers a good photograph of the choke cherry: https://www.ontario.ca/page/chokecherry
Pin cherry, Prunus pensylvanica
Choke cherry, Prunus virginiana – flower clusters in pendulous racemes
European bird cherry, Prunus padus – – flower clusters in pendulous racemes: