>>2373058here are the seeds used at umn (
https://coveritup.umn.edu/seed-mix), southern ontario is pretty similar but depending on your town there may be some that are no-gos though most should be fine to plant (i can't see any issues, but i've not been home for a while so i'm not sure what's on the watchlists these days). birch and spruce saplings should push the buckthorn seeds out of place, and cherries will give you even more diversity in the seasonality of your sun blocking and will be basically a 1:1 swap for the buckthorn because of their similarities. after a few years you should be able to grow a lovely patch of forest flowers and forageables without needing a whole woodlot. :)
https://landscapeontario.com/perennials-for-your-garden https://www.thespruce.com/groundcovers-are-low-lying-plants-2131058 https://www.thespruce.com/long-blooming-perennials-2131857 if you need any other varieties, these should also suit the region well and give you and yours something nice to look at all summer long. Hg can rise with increased canopy cover in clay and loam rich soils, so be sure to investigate local plants with high nutrient uptake/soil 'cleaning' properties after about two years of having full canopy coverage too.
