The extensions of the pages won't matter, provided you're able to actually put the canonical tag itself within the of the page.  If you put in the , it'll be ignored.

You only need to put the canonical tag on pages that are duplicates of other pages.  You'll need to be able to specify the correct href for the canonical tag for each page, which is the full URL of the page it's a duplicate of.  If you only have that level of control to place this only on the duplicate pages, you are still ok, as you can have a page rel=canonical to itself (according to Matt Cutts here).  So if all the duplicate URLs and the original URL all rel=canonical to the original page, it should work.  If you don't even have that level of control, you might not be able to use the canonical tag.  I hope that's what you mean by "Master Page"... if you have each master page rel=canonical to itself, it sounds like it could solve this for you.

FYI, if you can 301 redirect these duplicate pages to the original page, that's the preferred method of resolving duplicate content issues.

Looks like you asked this question twice... some answers are over at http://www.seomoz.org/q/should-i-put-a-promo-code-directly-into-adwords-copy.

I don't think it's necessarily bad.  I'm just not sure it's as compelling as stating the savings and an expiration date in your ad.  You could try running an ad with the code, and a similar one without it, and see which does better.

If the user doesn't write down the code and later forgets it, they may might not be able to find it again!  If you do use a promo code in your ad copy, make sure it's easy to find on the landing page, or automatically added the customers cart when coming from your ad.

One article I found reinforcing this: http://certifiedknowledge.org/blog/be-careful-of-using-discount-codes-in-your-ad-copy/

I'm not sure about your HTML sitemap; I don't think HTML sitemaps are a supported format for you to submit to Google (I don't see them on sitemaps.org).  You just need Google to crawl this page, and all the pages it links to?  There is a plain text format (see here) that is allowed for sitemaps.  You could probably change your HTML sitemap pretty easily to that format.

I'm pretty sure you're allowed to submit multiple sitemaps, but I can't find anything concrete saying you can or can't.  The Google Webmaster Tools UI seems to support it, so my guess is that it would be fine.  Try it and see if it works?  You could also create a sitemap index file that references both these sitemaps.

You can read more about sitemaps on sitemaps.org.  According to the Google help doc here, they adhere to these standards.