buckworks - 1:48 pm on Sep 25, 2011 (gmt 0)
The light box might be a policy concern, depending on what you're doing with it, but merely having variables in your URLs used for Google ads should cause no problems for your organic SEO. Especially not if you're using the canonical tag correctly.
For starters, URLs that appear within AdSense ads (or other ad networks) do not get normally counted as backlinks.
If a user copied your landing-URL-with-variables and posted it directly on a regular page someplace, that would put the URL into organic circulation, but in my experience that doesn't happen often enough to be a practical concern, not even in the days before the canonical tag was developed.
My advice: Make your decisions about what landing pages / URLs to use for AdWords based on the logic of your sales funnel, not organic SEO worries.