We've spoken of this before, Andy. There is a physical description of Jack Reacher in pretty well every book about him. Here's a typical one from <i>Bad Luck and Trouble</i>...
"Six-five, two-fifty, hands as big as frozen turkeys...forearms like Frankenstein's monster."
And, later in the same book...
"His arms were like a gorilla's only longer and thicker."
Elsewhere, one of his women friends describes him as being "like a six and a half foot condom stuffed with walnuts", which Lee Child actually ‘borrowed' from a book by Clive James. There is not a shred of doubt what this guy looks like in the author's mind.
Of course, film directors - and readers - are not obliged to stick to a writer's depiction of any given character...so, Kevin Spacey, if you like...but there can be only a handful of actors around who fit the bill as far as Lee Child is concerned. Arnold Schwarzeneger at one time possibly, but, for me, Kevin just ain't Jack Reacher!