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I tend to agree with Moosa that cross-domain canonical can be a bit unpredictable. In theory, it can work well for syndicated (or anything like syndicated) content, and I've heard of examples where it worked very well. Some big newspapers use it, for example. There are also cases where Google can choose to ignore cross-domain canonical, so sometimes you have to try it and see. The good news is that the risk is low - worst case, it just won't do much. Of course, it can keep your other sites from ranking for that same content, but it sounds like that's what you intend anyway. My gut reaction is that it should boost the main site somewhat - I just don't know how much. My only warning about the 301-redirect is that these approaches are very different in one respect - the visitors. A 301-redirect will take visitors from one site to the other. A cross-domain canonical only impacts Google. The 301-redirect is typically more powerful in this case, but it may not be appropriate for your scenario.