This is one of them.
A quick peruse of the Ontario weeds website lead to a firm ID. This appears to be Canada Fleabane to my untrained eye.
Follow the link to weed index. You will find many common, and not so common, weeds with great coloured pictures of each. Descriptions and habitats are listed.
If you are still stumped, you can send in a picture of the weed to get postive ID.
It is an outstanding tool. Well done Mike.