Having flown from Toronto to Aruba and back over the past 6+ years, I have certainly had my ups and downs with different airlines (pun intended) Service now is better from Toronto than it has been in past years. Previously Air Canada only flew in between Dec15--April 15th (the high season) and primarily to accommodate Air Canada Vacations customers. Last year things changed. WestJet signed an agreement with Aruba to fly in off season and have been doing so this year. This awoke Air Canada who also started off season flights. Air Canada leave every Saturday around noon and WestJet fly on Sunday. Both of the airlines operate on a charter basis for Sunquest and other tour operators. When hotel/flight packages are not sold out, remaining seats on the aircraft are then offered via the likes of itravel2000, TripCentral etc. The prices tumble as the departure date nears. Today's WestJet flight dropped from 499 to 299 to 169 (plus taxes) over a 2 week period. It is my understanding that WestJet is studying passenger loads and demand to determine whether a service offered by them direct is feasible.
At present, Canadian carrier options are Air Canada, WestJet (both through Tour operators.) There is a new entrant into the field starting in early November...that is the classy Sunwing Airlines. Their fares are reasonable and you can book direct with them. Take a look at their site www.sunwing.ca ...go to flights and enter your dates. You will see that their fares vary depending on date. WARNING: As all of these are charter flights the duration of the trip is generally limited to a maximum stay of 14 days. I do understand that with Sunwing you can apply to have that extended depending upon space.
Hope this enlightens the Toronto to Aruba flight situation with these charter operators. Note that there are also the scheduled airline flights and if you shop and choose a non peak day for travel it is sometimes possible to get even better fares.