Interesting, but this film (along with Videodrome and Existenz) convinces me more and more Cronenberg is perfect to do a Philip K. Dick film--or maybe he's been doing them all along, and no one's noticed. Scanner's hero is the Dickian loser and outcast, who can't fit in because he has a unique perspective of the world (he's either schizophrenic, or has enormous psychic power, or both). The forces chasing him are the kind of vast governmental/corporate forces Dick builds into his novels. Even some of the dialogue resembles the Dickian style of pulp metaphysics, of cheap SF terms mixed with thought-provoking ideas--"Scanning isn't the reading of minds, but the merging of two nervous systems, separated by space." And the ending--well, I don't know if Cronenberg has read Dr. Bloodmoney, but the climax to Scanners bears a more than passing resemblance to the climax of that novel.
One more thing: people have mentioned the relative incoherence of the plot (though this was probably mostly before they saw his next work, Videodrome); actually it does come together, sort of, but you have to assemble the pieces in your head; Cronenberg doesn't give you much in the way of help. The confusing plot does help give the film an air of confused terror, of untrustworthy forces beyond your control, malignantly manipulating your life--or at least the story, for some 100 minutes. A great horror flick.