<p>If we develop a winform app using an MVC architecture, it should not be too hard to change over to WPF at a later date, correct?  </p>

Well designed WPF application heavily leverage data-binding. As such, you might consider using classes such as ObservableCollection and others and implement IPropertyNotify when designing your model.
Look up some references to the M-V-VM pattern advocated by Microsoft product groups (e.g., Blend) for more information.