If your PPC pages use a part of the content that's already on the SEO page (duplicated content) I would noindex those pages. Trying to get both pages indexed can only backfire. A other quick indication, if those pages are only attainable through your Ads and offer no new information to users who started there visit on the home page I would also noindex them.
If however, your PPC pages offer unique value to your visitors they can't find on other pages on your website (or on your organic landingpages) you could let them get indexed.
For point 2: Having a useful internal link structure is a best practice for SEO. If your pages offer unique value I would add them (in a logical way) to your internal navigation structure. If however they **do not ** offer unique value those links won't be useful for your visitors and will only be there to support your SEO. In this case it won't do you any good.
For point 3: Your building a triangle. It doesn't make sense to try to give your PPC pages any status through internal links and then giving a canonincal to merge any status with your organic pages. Either way, I would not canonical those pages. Give them noindex or treat them like a normal page.
Since this question is pretty old, I would love to know how you handled the situation!