Not sure is this a PeeGee hydrangea. Can I cut it down in the fall or wait until Spring. Live in Toronto.
Yes, this appears to be a Hydrangea paniculata or panicle hydrangea. Late winter or early spring is the time to cut these shrubs all the way back to the ground. Panicle hydrangeas will produce much larger blooms if pruned hard like this each year. Many gardeners opt for smaller blooms on sturdier stems. To reduce flopping, leave a framework of old growth.
For more information you may wish to go to https://www.torontomastergardeners.ca/askagardener/hydrangea-paniculata/
There is also a Gardening Guide that may be of interest to you: “Growing Hydrangeas – A Toronto Master Gardeners Guide”. https://www.torontomastergardeners.ca/?s=hydrangeas