In terms of page format the typical page sizes in Europe are A4 (8.268" x 11.693") and A3 (11.693" x 16.535") similar to letter and 11x17 respectively. I recommend formatting your portfolio to these dimensions. Especially if you are submitting a digital portfolio and they happen to print it without scaling. At best it looks weird and at worst it cuts off some of your text or contact information.