AirHint found the following cheapest return flights from St. Louis (STL) to Toronto (YYZ) in September 2025 (see full year).

Return flights

29 Sep - 02 Oct	Frontier Airlines
30 Sep - 03 Oct	Frontier Airlines
22 Sep - 24 Sep	Frontier Airlines
24 Sep - 01 Oct	Frontier Airlines
20 Sep - 23 Sep	Frontier Airlines
29 Sep - 02 Oct	Air Canada	direct
20 Sep - 21 Sep	Frontier Airlines
28 Sep - 01 Oct	Air Canada	direct
24 Sep - 01 Oct	Air Canada	direct
17 Sep - 19 Sep	Frontier Airlines
20 Sep - 23 Sep	Air Canada	direct
20 Sep - 21 Sep	Air Canada	direct
17 Sep - 19 Sep	Air Canada	direct

Also check the deals for one-way flights from St. Louis to Toronto in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from St. Louis to Toronto in September from 302€

Return flights