You might want to check following 2 website shopping cart services we offer to find out one most suitable to your requirement:

Dropshipsite.com : We list all our products and we maintain inventory, your responsibility is to promote your website and collect orders and then place that order on ewis.ca and we dropship to your customers. You can not add your own products in shopping cart however, you can add your products in HTML pages with PayPal payment buttons.
Click here for more information.

ASPShopCart.com : We give you blank shopping cart with ability to add products through admin panel, you can list any of your products or our products. You will be responsible to list, maintain and update product inventory. Gold and platinum package come with bulk product import feature using which you could upload product in bulk directly from tab delimited text file (from microsoft excel file). Bulk upload feature also allows you to import all EWIS.ca products in your shopping cart with click of a button.