Japan Islands Cruise no worries with air. A quick check showed it will not be a problem there will even more options that those shown below.
USA to Sapporo
Connections to Sapparo from Tokyo, Osaka, Hong Kong and Taipei
American, Delta and United then connnecting airline
(AA and Japan air are partners)
Connections from Guam to USA via Honolulu, Japan
United and Delta fly from Guan
