AirHint found the following cheapest return flights from Ontario (ONT) to San Juan (SJU) in September 2025 (see full year).

Return flights

23 Sep - 26 Sep	United
18 Sep - 21 Sep	Frontier Airlines
20 Sep - 27 Sep	Southwest Airlines
04 Sep - 06 Sep	Frontier Airlines
28 Sep - 05 Oct	Southwest Airlines
19 Sep - 23 Sep	Southwest Airlines
26 Sep - 04 Oct	Southwest Airlines
20 Sep - 26 Sep	Southwest Airlines
17 Sep - 24 Sep	Southwest Airlines
06 Sep - 18 Sep	Southwest Airlines
06 Sep - 11 Sep	Southwest Airlines
01 Sep - 11 Sep	Southwest Airlines

Also check the deals for one-way flights from Ontario to San Juan 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 Ontario to San Juan in September from 287€

Return flights