So there isn't much I can tell you about him that you don't likely already know. We speak often of "inning eaters" here; supposedly, that's the reason the Cubs signed Edwin Jackson, only he turned out to be a guy who spit innings out instead of eating them.
The Cubs have gone on record as saying they'll be looking into signing pitching help, but the money has to be "within reason." Reading between the lines, that could mean David Price isn't coming to the North Side. Instead, starting pitching help will likely come from a group that includes Leake -- mid-range, No. 3 or No. 4 starters who can, in fact, eat up some innings. The Cubs have a very good top of their rotation in Jake Arrieta and Jon Lester. The problem, as was found during the NLCS, is the rest of the staff.
Signing Leake, who can give you around 200 relatively injury-free innings every year, might be a good way to go. He did spend a short time on the DL in 2015, but that was a hamstring issue, not anything arm-related, and he came back and ate up innings for the Giants (49 in eight starts) after returning.
Leake made $9.775 million in 2015, so could be affordable in, say, the 3/40 range. At this point I'm kind of on the fence about him, but if he could pitch the way he did the last three years (3.59 combined ERA in 94 starts) he'd be a good addition to the staff. He also doesn't walk many (his 1.161 WHIP in 2015 was a career-best). He has the advantage of not costing a draft pick, as he was traded during 2015 and as such, could not get a qualifying offer.
Oh, and wish him a happy birthday -- he turns 28 today.