Maybe something in this article would sound familiar?

It does sound like a rust fungal disease, and according to the article, Quince rust can affect Saskatoons with juniper or cedar as an intermediary host.

Here is a link that might be useful: Rusts

Yeah, it's rust. Saskatoons are extremely vulnerable to it. You can try a sulfur spray to mitigate it.

Thank you both for your input.

northspruce I checked out the link you provided - although helpful it didn't quite cover the symptoms I'm dealing with so I had to rule out rust as the problem.

So I went searching online and bingo: Serviceberry gall mite. Small globular galls on the upper leaf surface, about 1/8 inch in diameter, usually reddish above and light greenish yellow below. The recommended treatment is horticultural oil to be applied in the spring when the buds are opening. It's too late for me this year but at least I can be prepared for next spring. Meanwhile I'm still plucking off any infected leaf as soon as it appears.

Thanks for the update. Good to know in future. Hope you get rid of it next year.

Interesting. I wonder if we have it in Alberta.