The green latern power is based on they willpower so it depend on how strong they will is. Droctor strange is one of the most powerful sorcerer in the marvel universe he has been toe to toe with powerful beings such world war hulk, mordo, mephisto, satannish, dormammu etc.
For a green latern to stand a chance against dr strange he will need to have immeasurable willpower.

Hard to tell on this one. Usually there are balancing acts between DC and Marvel characters. It could go either way. On one hand Dr. Strange would win and on the other Green Lantern would win.