Canadian Fin Fan (and B.C. Lions Fan) to the rescue. : ) The simple answer is they play 12 on 12, not 11 on 11 football. The slotback is the slot receiver. Most teams line up with two wide receivers and two slot backs on every snap. There is very little use of a full back in the CFL an the tight end is more of a big slot back in most formations, playing off of the tackle.
That should answer your question on the defensive side of the ball as well.
Just a quick note on Wake, I think Fin fans are going to love him and I think he will do well. This is not a gimic pick-up from a bad league. The CFL has a lot of quality players that just don't get a chance in the NFL or are a little raw in their ability. Just ask Jeff Garcia. Wake played two years and was the Defensive Player of the Year both years. He can play and I've been hoping for over a year that the Fins would give him a look. Should be a nice addition as an OLB in the 3-4 scheme. Catch some of his highlites on Youtube and you should get an idea of his athleticism.