Hi ... THANKS again everyone for their help! It's the original poster here.
Someone asked how old my child is ... he just turned 2 but he's fairly tall ... about 34". Hence, the seated height from bottom to shoulder being around 12". Didn't know we'd lose some height room when car seat was strapped down. Good to know and something else to consider.
Sadly ... I know if I get the Safety First Onside Air (which is basically the Scenera with the Onside Air feature as one poster advised), it won't last us very long.
However, I might just have to do it since it's a decent car seat for the price range. Don't really want to spend a ton of money on a new car seat which we'd probably only use for travel since we have our Britax at home.
Wish we travelled more but this is our 1st trip in about 5 years so yeah ... guessing, we'd outgrow the car seat way before we travel again! Besides, it's comforting that posters here have raved about the Scenera so I'd feel comfortable if I chose the Onside Air version. Too bad the prices are so much higher in Canada ... I think someone said they got theirs for $40?? Unbelievable!
I did end up looking into the Diono ... as one poster advised ... great carseat but it's pricey & heavy! Unfortunately, this won't be for us. I'm looking for a light weight car seat which would be easy to take on a plane. We're a Britax family and the Marathon we have is heavy which is why we're looking into getting a light weight car seat to take on the plane. Don't want to saddle my husband with lugging the Marathon around especially when we're taking our Graco Quattro stroller (another monster!). We usually take this when we need basket room (which we will need when we go to the parks) and it can be reclined down.
My Graco Quattro is not the best to push around (it's heavy!!) but it's old enough that I won't mind a bit of scuffing so long as there's no real damage from the air travel. However, as other posters advised, WestJet seems to be OK when it comes to gate checking etc..
By the way, I need a "roomy" stroller (which the Graco Quattro is) that reclines because I like to do diaper changes in the stroller. Have a germ phobia so don't really like to use public change tables ... spend too much time wiping them down and lining etc.. And, Murphy's law, after I go through this whole process of cleaning & lining the change table, my kids "freak out" on the change table ... some of them are "elevated" off the ground so they get scared and I can't do the diaper change ... too much thrashing around and crying! Just easier and less stressful for me to just put a change pad on my stroller and do the change! Sorry ... off topic!
Anyway, here's what I'm thinking for our "game plan":
a) Check in: luggage
b) Carry on: backpacks & car seat (send Dad in 1st so he can get started!)
c) Gate check: stroller (remember to ask for bags at luggage check-in counter)
d) Ergo Baby Carrier: most likely, I will "wear" my kid and put the car seat into our Graco stroller when we move through the airport. Hopefully, the stroller can also take at least 1 of the backpacks.
Thanks again everyone. Your comments/hints/experiences etc. are still welcome!