You can print A2 cards (5.5" x 8.5") and other card sizes on the Pro 200. I've printed thousands on the Pro 100 and recently just purchased the Pro 200 which works just the same.
To get it to work you need to disable width detection as mentioned here: https://ij.manual.canon/ij/webmanual/ErrorCode/PRO-200%20series/EN/ERR/1062.html?ref=1062
In Photoshop (or whichever software you are using) create a 8" x 10" document. Center your 5.5" x 8.5" design and move it flush to the top. You can now print this using the 8" x 10" Borderless setting with the printer. This also works with designs that go past the border as shown in the attached screenshot. There you will see the dotted line which marks the 5.5" x 8.5" paper and the design which extends slightly beyond. This way you can set the "Borderless Extension Amount" to minimum which gives you the most accurate print. Alternately you can make your borderless design exactly 5.5" x 8.5" and then set the borderless extension to 2 or 3. But I've always used the first method.
Do note that with this "trick", borderless printing only works on the leading (top) edge and the sides. The trailing edge (end) will not print past the border. This is generally not a problem as only the front (top) half of a greeting card generally has the design that may need to be printed borderless. So make sure your card design is on the top in the document. If you have cards that require borderless printing also for the trailing edge (back of the card) then you can stick a post-it note underneath so that it sticks out slightly at the end (just a 1/4 inch is enough). This fools the printer into thinking the paper is longer than it actually is and thus print past the end. If you're printing a few this is a suitable trick.
Also, depending on how many borderless cards you print and how heavy the ink usage is, you will at some point have to clean the bottom plastic ridges that surround the ink sponge (foam strip) which you see when you open up the printer. Over time the ink gradually builds up on those ridges that are right on the outside of the 5.5" paper. If you do not clean them as needed (with a cotton swab and some water or alcohol) the build-up will eventually smear the underside of the cards.
If you have any questions feel free to ask.
