I managed to do this by following the instructions for embedding Google Map Engine maps on this page:
It requires you to update your sharing settings for the map to 'Public on the Web' before you are able to grab the code snippet.
Snippet looks like this:
<iframe src="https://mapsengine.google.com/map/u/0/embed?mid=xxxxxxxxxx" width="100%" height="100%"></iframe>
Once you've copied the snippet, add an embed component to your Webflow page and paste the snippet there. Make sure to edit the width and height parameters to suit your needs.
I dropped the embed component into a container and set the parameters for width/height to 100% on the embed component, so that I could define the width/height of the map by just changing the container properties and avoid having to do it via the code snippet.
Hopefully that makes sense.