Harper could make his Premier League debut at home to Cardiff tomorrow.
Scotland international Allan McGregor is doubtful with a groin strain.
Bruce said: "I wanted Steve for his experience because Allan McGregor has plenty and he has played games for Scotland but he has no previous experience with the Premier League so he is someone with proven pedigree and he played at Orient and he has still got that bit of class.
"The years have caught up with him a bit but he looks after himself but above all he is a really good lad to have around and a good pro.
"Wednesday was a great night for him and anyone who does 20 years deserves a night like last night and 52,000 for a testimonial is just quite remarkable. It's ridiculous really."
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