The Canon model has image stabilization which can come quite in handy when handholding and not using a tripod. It also has a UD element which may improve the chromatic aberration on that lens. The Canon has 50mm longer reach, which is a benefit.
The Tamron has full time manual focus which is nice to have.
One thing to point out, is that the Tamron is not a macro lens by any stretch, either is the Canon. I believe Tamron markets this lens as such, but don't buy into that.
From what I am looking at, the Canon is about $25 more on Amazon, so for the image stabilization alone I would say that is worth it. I don't see any compelling reason not to choose the Canon in this situation.
These are the two lenses I am looking at: