I'm high as one can reasonably be on Rasmus, and I think you have to do this trade in a keeper league. Harper has way more upside. Your keepers are going to be ridiculous next year. Anibal-Fister is a push. Mcab, Fielder, Braun, Pedoria, Stanton, Hanley, Harper, Ellsbury, Kershaw, Hamels, Greinke, CC, Halladay...who do you not keep off that list?
Harper may not be a top 6 option on that list for 2013. I would bet he easily makes the cut in 2014 and 2015, so you've gotta take him.
Here's the pitch on the way, a swing and a belt! Left field! Way back! BLUE JAYS WIN!