Selected answers from the Dumb SEO Questions G+ community.
Scott Clark: I would vote for linking topic-to-topic. You would not use anything but a self-referencing canonical here. Canonicals are suited to when you have duplicate or near duplicate content and want to focus on ranking one of the pages. Since either your blog or service could be ranked, you don`t need to do anything special there.
Michael Martinez: Why can`t you link to both? Do you have a specific context for the links in mind?
Michael Martinez: I don`t think it`s worth your time to figure that out. Create the Website you would want to use if you are a visitor. Let the search engines do some of the work.
Shane Lowry: Internal linking to any related posts is good for seo
Mal Ö Tonge: You can use either or both, but if using both be careful to not compete against yourself. the last thing you want is your page to be ranked for a keyword that a blog post should be ranking for.