Colin out - Stephen Fry in!
...At least they should consider him
shareMmmm...I like Stephen Fry and it would be good to see him have some sort of connection with the movie, but I don't really think his voice sounds all that right for Paddington. If they thought Colin sounded too old, imagine what they'd make of Stephen...who's a little older than Colin.
How about either of co-star Peter Capaldi's immediate predecessors as The Doctor? We've seen both Matt Smith and David Tennant capable of childlike enthusiasm.
Or there's Hugh Laurie, who, as scuttlebutt had it, was approached for the voice before they cast Colin. In his natural English accent, he can sound earnest and gentle. (Just look at his role as George in the various Blackadder series--especially Blackadder Goes Forth.)
Then there's Tom Hiddleston. His voice has what I think is the right sort of pitch. Besides, we need someone who can sound gentle, vulnerable and guileless. Tom played a character who tried to take over Earth and subjugate its people, and spearheaded an attack that left hundreds dead...and still had swooning fangirls calling him a misunderstood little bunny rabbit. If THAT doesn't show he can play it gentle and likable, I don't know what does.