[BMW Rider]

If you like the vertical grain then that is how you should orient it. There are many possible solutions to the joint problem, You could choose to make it frame and panel style, use a moulding to cover the seam, use an accent filler to highlight the seam or a small groove to do the same. If you truely want a single clean panel, that should be doable with carefull jointing of the seam. Usually the finish veneer of a cabinet grade plywood sheet will be multiple stips and not a single wide piece of veneer. The veneer is bookmatched to minimize the jointline visibility. With carefull selection of the plywood and choice of where you cut the sections of the panel from it, you should be able to visually eliminate the joint in much the same manner. Then its just a matter of making a nice tight flush joint between the two pieces. Some manner of joinery to reinforce the joint, like a tounge-and-groove. rabbet or biscuits will be needed to ensure the joint does not open up later.