Willis said that he was surprised by the inclusion of Bopara, with the batsman averaging just over 30 in both Tests and one-day internationals.
"I doubt I'm the only one who is a little bit surprised to see Ravi Bopara back in the England fold," Willis wrote in his blog for Sky Sports News.
"Bopara's had a difficult time away from cricket in the last 12 months but he must be approaching the last-chance saloon after averaging only a fraction above 30 in Test and ODI cricket despite repeated opportunities to impress.
"With two new, white cricket balls in operation in ODI these days there has to be an emphasis on picking proper front-line bowlers. Looking at the squad now, I'd say that Bopara plus Jonny Bairstow, James Tredwell and perhaps Chris Woakes will be the four to miss out from the 15."
England start their Champions Trophy campaign when they take on Australia on June 8.