The airline you are referring to is Flair. They are currently being investigated by the Canadian Transport Agency for possibly "not qualifying as a Canadian airline" due to there ownership structure and plane leasing etc. I know they've attempting to align themselves with the rules and they seem to think they'll be fine. I have a flight to Orlando (that I moved from March Break) in August so I'm obviously hoping that everything works out.. I would wait a few weeks if I was going to book with them and see how it all pans out.
Swoop (owned by Westjet) is another low cost Canadian carrier.
Also, the charter airlines (Air Transat, Sunwing) have some domestic flights, especially during the summer tourist season.