If people are worried about size (despite the fact that his skill is bonkers) remember that Kane was smaller than Marner in his draft year. PK = 5'10/160lbs. MM = 5'11/165lbs.
I know, I love Marner. But there are always going to be people obsessed with size and I'm telling them that it isn't the be-all and end-all, especially when it's players' sizes coming out of juniors. There's no reason why Marner can't be a top-5 pick.