Hi, I live in Toronto, in what used to be East York. I usually cut back a lot of the plants in the garden, although I do leave some for the birds.
Is Oct 11th, Monday of next week, too early to start this process?
You are asking a reasonable question for all Toronto gardeners this season. With the mild weather we are enjoying, we may want to remember the needs of our gardens are weather dependent, rather than calendar date motivated.
Toronto Botanical Garden has a good summary of fall tasks, as does Landscape Ontario.
Most important is observing and waiting until the plants become dormant, which will vary with each type. Leaving hydrangeas and sedums for winter interest is fine, as you may prune these severely in spring. Edible seeds and berries left for birds will enhance your garden too.