What is good approach of implementing web widget

Question

I have a dillema of the way web widget apps should be implemented.

Scenario is that website A should present content of website B as a widget. Lets say that the widget content type is webshop, so all that a webshop can offer will be inside a widget. Items, cart, login, checkout, etc, but no redirection to other site. Window stays on Site A. There is no interaction between websites. No data passed from one to another.

Technologies that will be used are .net Web API as server side, angular as js framework, and all will be implemented as single page app.

I see two scenarios.

1. Website B will be embeded in website A through iframe
2. All js, css, and initial html will be somehow embedded into website A and make calls to WebApi services.

I'm not clear how 2 should be done. Giving some bundles of JS, CSS, and HTML to Site A to implement is kind of overhead for both me and site A, and I see a lot of troubles there. Maybe it all should be injected dynamically somehow. On the other side..iFrame...this seems like a right scenario for use of iframe, but is it?

Any thought is appreciated.