Sub-domain and redirects

[gpeters]

I have two ecommerce sites I’m launching where I will have one site for the US and one for Canada. I don’t want to have two domains but rather have www.mydomain.com redirect to www.mydomain.com/ca_english/ when some one clicks on the link for Canada. I would do the same for French www.mydomain.com/ca_french/

I need some ideas and help in setting this up

Thanks