GameStop CEO Ryan Cohen has a bold plan to buy eBay, a much larger company than his. And he’s offering a lot of money—$56 billion, or $125 a share. There’s the rub: eBay stock is hovering around $108, a sign that Wall Street doubts Cohen can pull off the deal. Prominent money manager Bill Smead, whose firm has been an eBay stakeholder for nearly 20 years, is skeptical, too.