The phrase "marching cannons mouth" can refer to someone who talks loudly and assertively, often making sweeping statements or demands. Synonyms for this term might include "blustering blowhard," "bombastic braggart," or "pompous windbag." Other possible options include "grandiloquent gasbag," "arrogant autocrat," or "dictatorial demagogue." Additionally, some might use terms like "domineering despot" or "overbearing oracle" to describe someone who fits this description. No matter the phrase or term used, the implication is that the individual in question is someone who enjoys hearing themselves talk and imposing their opinions on others.