The Game -- Banned from Canada Over Gang Ties

The Game was detained in Canada for several hours yesterday, TMZ has learned, before his ass got deported back to the U.S. -- and we're told, it's all because of the rapper's alleged gang affiliation.

A rep for Substance Entertainment Group -- the promotion company behind Game's tour in Canada -- tells TMZ, the tour promoter got a call from Canadian Customs while Game was on the plane on his way to Canada.

We're told customs informed the promoter that Game would be denied entry "due to new information received that Game is affiliated with organized crime and is an active member of the Bloods street gang."

The rep claims Game was blindsided by the last-minute red flag -- telling us, concert organizers had secured all permits and approval weeks ago to get Game into the country.