I made a deal with a guy. I will give him advertising on my site for his business. He will give me permission to reprint the articles that appear on his site (he wrote them). I was looking for a lot of content quickly and this gives it to me. But now I'm reading in order to not get dinged by Google, I need to pass any SERP power off to his sit using the rel="canonical" tag in the head of each page. Is this true?
Yes, you must use canonical URLs for this content. It is pure duplicate content which exactly is what Google does not want. So you will be required to use conical URLs if you publish this content on your site. Failing to do so will likely result in your site being considered low quality due to its lack of unique content and your whole site will suffer for it in the rankings up to and including having no content available in Google's index.
You want to ask yourself what's the purpose of having these articles on your site?
Since the articles have been authored by someone else and already published on another site, Google won't give you "credit" for them so they won't help your site build relevance or authority. Therefore, they'll be no help in driving traffic because they'll likely not appear in search results.
If you're publishing them on your site for your current visitors, or as landing page content, that's a valid use, if they offer value to the people who visit your site.
To be safe, you absolutely should use the rel=canonical tag on these. This is your way of telling Google you're not trying to claim credit for them as your original content. It's sort of like putting an image credit under a photo, so people know who actually took the picture.
You should still have your own original and useful content. If the majority of your content is duplicate (even if it's used with permission and with the canonical tagging) your site still risks a lower quality rating because it offers nothing unique or different.