If I understand correctly, you're saying that you want the canonical tag to point to the first page in the series of pages, but you also want to use rel="next" and rel="prev"?
My advice on that, for what it's worth, would be don't do it that way. The whole point of using the rel="next" and rel="prev" attributes is that you are telling search engines that you want them to index the next and previous pages as separate pages. But by having the canonical link element pointing to the first page, you are telling search engines that you want them to treat all of the subsequent pages as duplicates of the first page and ignore them. So that's a contradiction, and I'm not sure how search engines will interpret it.
If you're going to use rel="next" and rel="prev" you should have the canonical tag point to the actual full URL of whatever page is being displayed, as you were originally doing if I understand you correctly.
Also, there's no need to use a TV for the canonical unless you really want to for some reason - generally it's better to use this:
<link rel="canonical" href="[[++site_url]][[*id:isnot=`[[++site_start]]`:then=`[[~[[*id]]]]`]]" />
See this thread:
http://forums.modx.com/thread/?thread=44222&i=1&page=1