The spray is purely for convenience.
You usually cannot buy Canola Oil in small quantities (usually it's in a 16 oz or larger container), and it can spill/be messy. The dark metal sides of the spray bottle will also preserve the oil longer, since it doesn't allow light to penetrate and degrade the oil. If you keep your Canola Oil bottle in a dark cupboard, this wouldn't be an issue.
The spray helps prevent a mess, as you can control it a bit better, but it's entirely unnecessary and plain Canola Oil will do just fine. After all, it's what folks have been using for a very long time, well before the spray was invented.
I wouldn't use PAM Spray, it contains other ingredients other than Canola Oil. Mainly:
- Soy Lecithin
- Silicon Dioxide
Most of the other ingredients will cook off when you season your pan - but using pure Canola Oil will be better for your pan.
Regarding seasoning your pan - I usually pour a generous amount of Canola Oil into the pan, knowing I can always wipe out any excess with paper towels.