The Cubs no doubt love having Sean Marshall on their pitching staff. He's an elite reliever, maybe the best non-starting southpaw in the game. He's also relatively cheap, due just $3.1 million in 2012.
Those qualities might make him popular at home, but they make him thoroughly attractive elsewhere in MLB, too. If the Jays win the Darvish bidding, they should grab Marshall and make themselves a bullpen worthy of true contender status.
In return, the Cubs need not stop with Asher Wojciechowski, though he is a solid pitching prospect. Drew Hutchison is a smaller, lower-upside hurler, but throw him in and the Cubs get just the right blend of risk and reward potential from this deal.
The market for players of Marshall's caliber was set this summer, when Mike Adams merited two strong pitching prospects in a trade from the Padres to the Rangers. If you think Cubs GM Jed Hoyer will have forgotten that deal, think again. He made it, after all. Marshall is of a slightly lesser pedigree, and is under control for just one season, so he will command a slightly less impressive pair of pitchers, but this deal strikes the proper balance.