Strictly speaking, Visual Studio doesn't integrate with other GUI toolkits; the toolkits may integrate with VS. For instance, Qt provides integration with Visual Studio, so you can develop Qt apps from within the VS IDE.
Visual Studio itself supports development for several frameworks:
- Raw Win32 (OK, not really a framework, but I thought I'd mention it for completeness; and there is a dialog editor)
- MFC for C++ (crude support for GUI design)
- WTL for C++ (no support for GUI design, AFAIK; it's all code)
- Windows Forms for .Net
- WPF for .Net
I don't know that it makes sense to speak of a default framework. Windows Forms is, I think, the most commonly used today, with WPF rising in popularity (or maybe I'm out of date).