You don't say where you are booking from/to and the price that you are seeing but I would guess that you can probably do better. It is still very early and I would think that most of airlines flight plans and times have not been finalized yet. If you are traveling from a major Canadian city and are seeing only one flight it is pretty much a certainty that there will be more.
As for timing to book at the lowest possible fare I am not an expert but after speding quite a bit of time checking west jet's fares I seem to notice that everytime they announce a new seat sale they seem to release a new block of seats. So for example on a monday you could check and see that you they are have 5 seats left at the lowest price of $189.00, on wednesday they announce a new sale and now the same flight has a new lowest price of $129 and they have 15 seats remaining at that price. I would advise you to subscribe to get Jetmail from west jet and also to get air canada's e-mail fare alerts. That way you should be notified each time they announce a new sale.
In my experience there seems to be a bit of a "sweet spot" about 2-3 months in advance of your travel when the fares seem to be the lowest HOWEVER I never travel over xmas so I couldn't really tell you if this holds true over this time period.
Another tip, try westjetvactions.com. You will have to book a car or hotel or both along with your airfare but when I checked for my trip to orlando they consitantly offered a car rental and flights for less money than they charged for just the (same) flight on westjet.com