How much weight could I gain?

I am a somewhat lanky 18 year old. I have always been physically fit with very minimal fat on me. I am 6' 5" and currently weigh 189 lbs. I played junior hockey last year and stayed at pretty much the same weight the whole season. I am considering going back for another year and to be successful I would have to gain weight. Training camp would start in late August and I want to know how much weight I could possibly gain if I got a personal trainer and ate a hefty portion.