Down here some of the guys will dethatch in the spring and aerate in the fall. I dont see why you want to dethacth AND aerate a lawn unless you have a seriuos thatch problem. I would recommend an aeration in the fall, interseed (if needed) and fertilize.
I will mow the lawn first before aerating.
Hope this helps. I dont know what your situation and conditions are up there in Canada so I can only tell you what works down here.