I know this is an old question, but I have a simple solution – just make the first child of your CardView an ImageView and specify the scale type to fitXY. You can get rid of the extra CardView padding by setting cardElevation and cardMaxElevation to 0dp:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="200dp"
app:cardCornerRadius="4dp"
app:cardElevation="0dp"
app:cardMaxElevation="0dp">
<ImageView
android:src="https://stackoverflow.com/questions/27299291/@drawable/your_background"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitXY"/>
<... your layout
.../>
</android.support.v7.widget.CardView>