Hi, Christine~  I'm not the pro here, but I can answer your question and offer a bit of advice. First of all, you must create your own borders before submitting your design. Remember that a 5x7 or 7x5 design will not end up at the same proportions if you simply click a button and add a border. Also, those cards that are printed at a Target store will automatically have a white border added as part of the printing process. This may not look good if you overdo it with borders, frames and other additions to your designs.
Second: I have learned from my own experience with GCU that the Reviewers are not overly fond of borders unless they greatly enhance the image. There must be a reason for adding one.
Often, I've had some artwork or a photo of mine that I wanted to use for a card, but the image was square or not proportionate to a 5x7 format, and cropping it to the proper format would not look good. Those are the times I have used a border, but I have made it enhance the image, not just surround it. Use borders sparingly or avoid them altogether (same goes for vignettes) and you'll be more successful.
Good luck!

Perfect advice, Ramelle! Borders should be used sparingly, generally speaking they detract rather than add to a professional greeting card image.