Well, Swoop (WestJet affiliate) operated Moncton/Edmonton 3x weekly last year, so they must have some idea what the market will bear.
Also, WestJet has reduced capacity on their Moncton/Toronto route, and have made a conscious decision to make Calgary their principle hub, so in some sense, the new Moncton/Calgary service is a bit of a replacement for the lost capacity on the Moncton/Toronto route.
Calgary might seem like a strange hub for New Brunswickers, but there are a lot of Maritimers in southern Alberta (or making connections to Fort Mac), and, if your ultimate destination is in the western US (California, Vegas, Arizona, Hawaii), then Calgary makes just as much sense as a hub as Toronto does.
I guess only time will let us know if this is a good business decision or not.