Tough call. I think Jonathon Jennings is the clear favourite, but what about Bryan (Burn 'Em) Burnham who had a sublime 208 yard receiving performance against the Bombers, and is arguably the biggest surprise to CFL observers this season. Or Manny Arceneaux, who is the toughest receiver in the league (just ask any DB who's been swatted by his stiff-arms) and sits 4th in the league in receiving yardage.
On the other side of the ball, there's Solly, who's mounted a great 'comeback' story from his Achilles tear last year, and leads the league with 105 tackles. Of course, when you mention Solly, Adam Bighill is always around the ball too, and is a worthy candidate with 91 tackles (and is often asked to drop back into coverage).