Load workspace using API

It sounds like you want to just call out to something that will do the load for you with what you specify. You can use  the IOperationFactory.instance.getLoadOperation(LoadDilemmaHandler) to get a load operation but you'll have to supply your own dilemma handler because the Eclipse dilemma handler isn't API. Otherwise, your users won't get the same kind of experience if there are issues during load that need user interaction.

I would recommend looking at load rules to achieve what you want without having to write your own plugin.

 In general using plain java API here is a trace of what is possible (used in RTC 4.0.7):

IWorkspaceManager workspaceManager = ...
IWorkspaceHandle workspaceHandle = ...
String sandboxPathName = ...
ISharingManager sharingManager = ...
IItemManager itemManager = ...

IWorkspaceConnection workspaceConnection = workspaceManager.getWorkspaceConnection(workspaceHandle, progressMonitor);
IPath sandboxPath = new Path(sandboxPathName);
ILocation sandboxLocation = new PathLocation(sandboxPath);
ISandbox sandbox = sharingManager.getSandbox(sandboxLocation, false);
List<IComponentHandle> componentHandles = workspaceConnection.getComponents();
for (IComponentHandle componentHandle : componentHandles) {
   IComponent component = (IComponent) itemManager.fetchCompleteItem(componentHandle, IItemManager.DEFAULT, progressMonitor);
   IConfiguration configuration = workspaceConnection.configuration(componentHandle);
   Map<String, IVersionableHandle> versionableMap = configuration.childEntriesForRoot(progressMonitor);
   versionableHandles = versionableMap.values();
   LoadDilemmaHandler loadDilemmaHandler = ...
   ILoadOperation loadOperation = IOperationFactory.instance.getLoadOperation(loadDilemmaHandler);
   loadOperation.requestLoad(sandbox,/*IRelativeLocation*/ null, workspaceConnection, componentHandle, versionableHandles);
   loadOperation.run(progressMonitor);
   sharingManager.deregister(sandbox, progressMonitor);
}