Getting SEO right for your ecommerce site means better positions in search results and more targeted traffic. By default ecommerce stores are hard to optimize for search because of the number of different products categories and not friendly url structure. Magento is not exception and by default it doesnt have very powerful controls over SEO of ecommerce store. However many 3rd party plugins exist created by the community of developers to eenable better Magento SEO optimization.
For example: Canonical URL for Magento
SEo Suite Pro