The attempted abduction happened on Wednesday afternoon near Levasseur Park in St-Constant, Que., on Montreal's South Shore.
Investigators say the man grabbed the girl, put her on his shoulder and began biking away.
After the girl's mother cried for help, a passerby intervened, stepping in front of the bike. He rescued the toddler, but the man who had tried to abduct her took off.
Police say the suspect is roughly 35 years old, about 1.82 metres (six feet) tall and approximately 104 kilograms (230 pounds). They say he is bald and sporting a goatee and appears to be of Latino origin.
Police are also asking that witnesses or people with additional information to call 1-800-659-4264.