For multi-monitor setups, we usually stretch the application window to cover all screens that we want to use and drag-and-drop the vertical splitters to be at the edge of the monitor. Several layouts have vertical splitters, but none of them would allow you to split 3 slice views. For that, you need to copy-paste the code below into the Python console to define and switch to a custom layout:
customLayout = """
<layout type="horizontal" split="true">
<item>
<view class="vtkMRMLSliceNode" singletontag="Red">
<property name="orientation" action="default">Axial</property>
<property name="viewlabel" action="default">R</property>
<property name="viewcolor" action="default">#F34A33</property>
</view>
</item>
<item>
<view class="vtkMRMLSliceNode" singletontag="Green">
<property name="orientation" action="default">Axial</property>
<property name="viewlabel" action="default">G</property>
<property name="viewcolor" action="default">#6EB04B</property>
</view>
</item>
<item>
<view class="vtkMRMLSliceNode" singletontag="Yellow">
<property name="orientation" action="default">Axial</property>
<property name="viewlabel" action="default">Y</property>
<property name="viewcolor" action="default">#EDD54C</property>
</view>
</item>
<item>
<view class="vtkMRMLViewNode" singletontag="1">
<property name="viewlabel" action="default">1</property>
</view>
</item>
</layout>
"""
customLayoutId=555
layoutManager = slicer.app.layoutManager()
layoutManager.layoutLogic().GetLayoutNode().AddLayoutDescription(customLayoutId, customLayout)
layoutManager.setLayout(customLayoutId)