Display Woocommerce products as well as Magento products in my main PHP site or CodeIgniter site

Yes . It is possible to display products from either woocommerce or magento to your PHP site. If your site is on the same server, you need to establish a database connection and retrieve products and related data using queries. If it's on a different domain, you need to use CURL. Create a script in PHP with which you can get the products. So my answer is yes, you can fetch and display wocommerce wordpress products as well as magento products in your PHP site or codeigniter site.