Ecoms sites are a little more diffecult to do great SEO o

e-commerce question. I am told and i read constantly that ecoms sites are a little more diffecult to do great SEO on. I am curious to hear what people think about using rel=canonical tag on all products and point them to the category page. i.e i sell fruit, so i would point all apple product pages to the apple category page, and all pear pages would point to the pear category page. Has anyone done this or seen it done? is it a stupid idea? would love to hear everyone and anyone`s thoughts SEO`s or Web site owners