You can use layerslider. You can add a slide and in the HTML/Video/Audio tab, you can paste your google map embed iframe code and then change the width to your required size.
Please see screenshot. http://prntscr.com/7hxeas
Here is some further information regarding this issue. http://codecanyon.net/item/layerslider-responsive-wordpress-slider-plugin-/1362246/comments?page=175#comment_4739008