Honestly, I think the easiest way would be to try to make friends with whoever moves into your old place (and/or the landlord for that place). That way you can arrange for them to hold your packages until you can pick them up if they do end up at their place.
You should also sign up with your current address for Canada Post’s automatic package notifications so you can stay on top of when they are in Canada Post’s hands. You might be able to talk someone at a post office into redirecting the parcels once you’ve got info on them (thought I think it’s a long shot).
Unfortunately CP seems to only offer parcel redirection services for businesses. Their mail redirect service (for regular customers) won’t be much help to you.
What slip? If you mean the “package delivery attempted” slip, those aren’t mailed – they’re left by the delivery driver at the location – so they wouldn’t be redirected by mail forwarding.