While purchasing the first ticket, you can mark the Return button, or after purchasing one-way, you can re-enter the system and purchase the return tickets by examining the reverse route sign with the reverse route sign.
When you search for flights between Calgary and Ottawa, all active companies and flight times on the date you entered are listed. You can find the cheapest flight tickets by sorting this list by price.
The most frequently used airline companies from Calgary to Ottawa are generally
KLM,
Freedom Airlines,
Delta Air Lines,
Westjet,
Air Canada,
Qantas Airways
are companies.