Manni was inspired to take up disability sport in 2004 after watching Finland's Leo-Pekka Tahti win gold at the Summer Paralympics in Athens. That year, at the age of ten, Manni took up paracanoeing. In 2010 he achieved his best paracanoe result when he won a bronze medal in the K-1 200 m TA event at the 2010 ICF Canoe Sprint World Championships in Poznań, Poland.