The former England Under-20 international still has over 18 months remaining on his contract at Old Trafford, but Bruce has admitted that he wants the stopper to commit his future to the West Midlands outfit.
The 56-year-old is quoted by the Birmingham Mail as saying: "We will do everything in our power [to buy him from Manchester United].
"He's got another year left on his United deal but he's going to find it difficult to break through there because of what they've got. Players like that need to find a platform."
On Saturday afternoon, Johnstone helped Villa to a 2-1 win over Fulham, the club's fifth league win in six fixtures.