I believe you fill the declaration at the newly installed machines and then print and hand to the CBSA officer who decides if you keep walking or if they have more questions. Not completely sure since I use Nexus. But I do know that on my previous flight from SFO-YYZ a couple of weeks prior, they did not hand out the forms.
I just googled it and for some airports incl YYZ, there is now primary inspection kiosks where you no longer need to fill out the paper declaration handed out on the plane.
http://www.cbsa-asfc.gc.ca/travel-vo...k-bip-eng.html
The video on this link specifically says no paper declaration required. You can also complete the declaration on a beta app before arriving at customs.
EDIT : I know the link says YOW, YVR and YYZ Term 3 but I thought that I saw somewhere that they had installed in YYZ, Term 1 too but I could be wrong. Perhaps someone who used the regular line can comment