It is very possible. However, you need to study the web sites of the various carriers in order to understand how you should pass them data in order to retrieve the shipment information.

Carrier tracking numbers have a different structure depending on the carrier, so you can quite easily parse them and understand the carrier they belong to.

There's however a caveat: some carriers might want tracking number to be passed via POST and not GET, and some might even check the referrer when a tracking request is issued. If this is the case with one of the carriers you use, you can't provide a direct link to you customers. Instead, you'll have to fetch yourself the information from the carrier's web site (using LWP for instance); then, you can parse the resulting page and display the shipment information on your web page.

For FedEx you might also want to take a look at modules such as Business::FedEx.

Hope this helps!

Michele.