Is this doable in a 2 week trip?
Jill, It should be, but it would help to have a few more details on your trip. Are you planning to visit only the Alsace and Belgium, or other locations as well? Where are you planning to stay in the Alsace? Cheers!
"Is this doable in a 2 week trip?" That depends on what you want to do. Post more details, and we can give more advice. For starters, a quick look at the Bahn website shows that a train from Brussels to Strasbourg is 5-6 hours with 1-2 changes. So that's certainly doable.
Where in Belgium are you coming from? Are you driving or taking public transportation? Where do you fly back from? Have you considered the Netherlands or western Germany (e.g., Aachen, Trier) as an alternative?