Canary pecking finger...?

Some reasons a canary may become more aggressive would be molting (many canaries get irritated easily at this stressful time), a cage being too small (24"width x 14" length x 18"height is the minimum size cage for canaries), hormonal problems, and possibly illness. In addition, he might be acting territorial over his cage. If this is the problem, I would get a hand-held perch and get your canary to hop on it. Take your canary away from its cage and then interact with it. A neutral area may be what your canary needs to get it more tame and less aggressive.