See this link.
http://www.airportwayfinder.com/wayfinders/yyz/?v=3_6
Go to
"Terminal 1 Connections" and then "International to International" for the video.

Your friend will go through "Customs B" - generally a cursory customs/immigration check. So more transit friendly than the US, but not as friendly as Europe.
But this only works if your friend arrives in Terminal 1 and their bags are checked through to Europe.

Hope this helps