The US passport is what you need to get back in. Unless you're already outside the US, I wouldn't leave until you have this important document. Technically, you could just reenter the US as a Canadian tourist with a Canadian passport under the VISA Waiver programm but why chance it?
The question is: Did he lose his passport for trying to evade the service in the Greek military?
The Travelling Artist - 2010 is rated/received certificates of: UK:PG
The Last Passport - 2009 is rated/received certificates of: USA:PG
Diplomatic Passport - 1954 is rated/received certificates of: UK:U
Passport to Destiny - 1944 is rated/received certificates of: Australia:G
Passport to Treason - 1956 is rated/received certificates of: Finland:K-16
Travelling North - 1987 is rated/received certificates of: Australia:PG UK:15 USA:PG-13
Passport to Murder - 1993 TV is rated/received certificates of: Iceland:12
Travelling Light - 1961 is rated/received certificates of: Finland:K-16 Finland:(Banned) (1964) UK:A
Passport to Paris - 1999 V is rated/received certificates of: Australia:G UK:U USA:G
Domenico's Passport to Love - 2008 TV is rated/received certificates of: USA:Approved
Forged Passport - 1939 is rated/received certificates of: UK:U USA:Approved USA:Passed (National Board of Review)