We are in east york and the cucumber plants get full sun.
The soil is triple mix. Drainage is very good as our garden is higher then our neighbours.
The plants in question are about 3 feet tall and spread is about 2 feet.
Thank you for contacting the Toronto Master Gardeners
A large number of fungi and bacteria cause spots on plant leaves, in a variety of colors, shapes and sizes. effect. Leaf spot diseases such as Angular leaf spot, Anthracnose, Alternaria leaf spot and Cercospora leaf spot are fungal diseases that cause spots to appear on the leaves of the cucumber plant, sometimes leading to stunted growth and lower-quality fruit.
It is not possible to identify the exact disease from a photo. The following links will take you to websites which discusses leaf spot diseases. By closely examining your plant and comparing the symptoms to the photos on the site you may be able to narrow down the possibilities. Generally though, these diseases are not serious. Help prevent the disease by keeping water from splashing on the leaves, sterilizing pruning and gardening equipment and removing debris in the garden that can harbor fungus. Because the disease can survive the winter, dig up and destroy infected cucumber vines after they have stopped producing fruit.
https://extension.umn.edu/plant-diseases/insects-and-diseases-cucumber-pumpkin-and-squash
https://plantvillage.psu.edu/topics/cucumber/infos/diseases_and_pests_description_uses_propagation
https://dengarden.com/gardening/Plant-Diseases-that-Affect-Cucumbers-and-How-to-Treat-Them
https://hgic.clemson.edu/factsheet/cucumber-squash-melon-other-cucurbit-diseases/