Involved in the biosynthesis of protopine and benzophenanthridine alkaloids. Catalyzes the conversion of the protoberberine alkaloids stylopine, canadine, and tetrahydropalmatine to their corresponding N-methylated derivatives. No activity with dimethoxytetrahydroisoquinoline, methylisoquinolinediol, norlaudanosoline, (R,S)-tetrahydroxyberbine, (S)-scoulerine or (R,S)-pavine as substrates. (S)-canadine + S-adenosyl-L-methionine = (S)-N-methylcanadine + S-adenosyl-L-homocysteine Inhibited by nickel, cobalt, calcium and magnesium. Optimum pH is 7.5. Optimum temperature is 37 degrees Celsius. Homodimer. Expressed in roots, leaves, stems and flower buds. Not expressed 1 day after seed imbibition but detected 4 days after imbibition and remains constant during seedling growth. Up-regulated by fungal elicitor. Belongs to the CFA/CMAS family.