I'm confused, after reading Matt Cutts, regarding the same web-page using parameters to display different categories / items.

e.g. 2 different formats of the URL,
/shop.htm?q=R (A to Z, list all items beginning with ...)
/shop.htm?id=11007(menu id, have numerous other categories)

This what I have at present:
<link rel="canonical" title="Buy Item beginning with 'R'" href="/shop.htm?q=R"/>
<link rel="canonical" title="Buy Items in Category" href="/shop.htm?id=11007"/>

But what is the correct definition please?

Many thanks,