Hey Vishalca,
Seats in Plus are first offered to all guests for a fee, during the check-in process and at the gate.

After the gate announcement, and any transactions are completed, unsold seats in Plus should be offered to WestJet Rewards Gold members for free.

Free upgrades are rare, but are provided on occasion to any guest based on operational needs, or perhaps as a guest service gesture (following a particularly bad IROP, or to a guests flying due to bereavement etc.)

All guests seated in Plus receive complimentary snacks, sandwiches and drinks when flight duration permits. Conversely, guests who purchase a Plus fare but are not seated in Plus do not receive complimentary food and drinks.

Let us know if you've got any other questions,
Darren