The Bears tend to prefer contracts that payout the same amount (or close to it) year after year through the life of the contract. At least that's what Cliff Stein (Bears contract negotiator/cap guy) has said at the Bears fan conventions the past few years. Guess we'll see soon enough.
My guess would be a decent signing bonus and a incentive heavy contract based off of receiving stats. Get X bonus (or salary increase) if you get 1000+ yards, make the Pro Bowl as a WR, get Y # of receiving TD's, Z # of receptions, that sort of thing. Perhaps even an 'opt out' clause that'd allow him to void some years of the contract if he achieves certain objectives.
But either way, glad to see they got it done!