Messi has already proved it. His record against the top 6 English sides speaks for itself. Ronaldo's record against the top 6 English is awful. I'm pretty certain that Messi would have no trouble scoring against the likes of Norwich, Newcastle and Burnley every week in that City team.
Of course he would but you'll always have those people saying he couldn't through a season in England. They are so wrong because football in la liga and the premier league is basically the same. And even though its a myth that players get kicked around more in the premier league messi is one of the toughest and most durable players ever