OfficialNerdCubed - Let's plays - 2,000,000 - No - English
The biggest one I would suggest is NerdCubed, He plays and messes about with indie games regularly and has a huge subscriber base, over 2 million, that would be a massive coup.
He plays all sorts of games so it's worth a shot I think.
Arumba - Let's plays - 118k - No - English
Personally, I'm a big fan of Arumba, 118k subs. Similar in style to quill18 and Northernlion, in fact they regularly do mp sessions on their channels. Plays a lot of grand strategy games such as Crusader Kings 2.
The benefit of Arumba is that rather than just messing about, he'd likely take it seriously and get into it (if it interests him). It would be good to have the game shown off to his subscribers as I think they are the type to enjoy the game.
For Arumba, I'd direct you to this video. They got a group together to play cards against humanity, in the same style, automation would be perfect for a video like this in that they can compete and joke at each others expense.
https://www.youtube.com/watch?v=ghWpu3VihPcIf you go for Quill18 and Arumba, then, then EnterElysium, MathasGames and shenryyr2 are also good to look at and all have60-120k subs or there about.
All of those play games still in development.
I'd second Robbaz, but consider modeling some viking horns for his copy XD