I have a Master page and a webpage that uses the Master page.
In both I have a Page_Load
event handler.
In which order are the Page_Load
The content page load event will fire before the master page load event.
See here for full order (MSDN: Events in ASP.NET Master and Content Pages)
Copying incase link goes dead:
The following is the sequence in which events occur when a master page is merged with a content page:
As far as MasterPage is indeed a user control all rules applied to it as for user controls:
Master pages run Page_Load() from the deepest level of nesting outwards. So your nested webpage will first run the page_load event.