JR Hokkaido train reservations will now be available online via the JR-East Train Reservation website as of 1 February 2017.
Travellers can now make advanced seat reservations for JR Hokkaido area Shinkansen (bullet-train), Limited Express and Rapid Airport trains.
Advance seat reservations will also be possible when using rail passes marketed for overseas visitors such as HOKKAIDO RAIL PASS or JR East-South Hokkaido Rail Pass.
Seat reservations made on the JR-EAST Train Reservation service will also be available for pickup in the JR Hokkaido area.
JR-East Reservations
http://www.jreast.co.jp/e/ticket/reservation.html