is it possible to redirect an URL www.siteA.com to www.site2.com/Default.aspx?SiteSource=siteA without changing the browser's URL?
Similarly, accessing www.siteA.com/Page2.aspx will redirect to the www.site2.com/Page2.aspx?SiteSource=siteA
is it possible to redirect an URL www.siteA.com to www.site2.com/Default.aspx?SiteSource=siteA without changing the browser's URL?
Similarly, accessing www.siteA.com/Page2.aspx will redirect to the www.site2.com/Page2.aspx?SiteSource=siteA
You can also use mod_proxy (or similar functionality for a different web server) so that the page your server serves is the same as the remote page. But this has some security and performance implications (you're letting the client make your server do arbitrary work copying data across the network from the remote server).
Use a HTML iframe to display www.site2.com/Page2.aspx?SiteSource=siteA, e.g.
More about the iframe tag.
server.transfer if on same server
If the URL doesn't change, it's not a redirect. However, you could create a proxy script that fetches the other page, rewrites any URLs within it, then outputs the result.