Cartoon Image Re sized/ blank border added - Photoshop/Lightroom

This is not a photo but a line cartoon. I need the a cartoon which is currently 2500 x 2536 resized to fit 698 x 400. Please see attached image file. As you can see the image is a white background and is currently square so it may be possible to add a white band on either side to make it the required size?

I have tried to re-size this myself but cannot get the whole image to display correctly. I wither loose the type on the box or the hat which is the whole message of the picture.

Please contact me if you need further info, I hope this makes some sense!

I need this done asap I am sure its a quick fix for someone who knows what they are doing. Please only respond if you can do this today.