Yes, CANTEEN is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, N 1, T 1, E 1, E 1, N 1.

Is it a valid word?

CANTEEN is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a flask for carrying water; used by soldiers or travelers
sells food and personal items to personnel at an institution or school or camp etc.
a restaurant outside; often for soldiers or policemen
a recreation room in an institution
restaurant in a factory; where workers can eat

Also: mobile canteen.