Container first - you will eventually need a large container but they can be started in small containers and potted on into ever bigger ones.. grapes really need a deep root run to give their best.
However they can be grown in containers successfully but will not crop as heavily. If you can plant it in the ground just outside the greenhouse and train it inside then that is the most practical solution while saving a whole heap of watering.
There are so many suitable varieties of seedless pink/red grapes to choose from including Beauty Seedless, Bronx, Canadice, Einsette, Flame, Glenora, Mars, Reliance, Saturn, Somerset, Suffolk Red, Vanessa. There are a number of others that will all ripen under greenhouse conditions.
A web search for any of these names will find you suppliers but Sunnybank Vines who hold the national collection could save you a lot of googleing.