Welcome to Flyertalk!
YVR Autism Resources
YYZ Magnus Cards (I believe they're similar to Social Stories - but they require an app so I haven't actually looked at them)
YVR, YYZ and MCO (but not YYC) are all
Sunflower Lanyard participating airports. You can pick up lanyards and/or a sticker at check-in. I should note that not everyone is familiar with it, since it's pretty new in North America.
YVR also has an
autism access sticker that provides expedited security screening, but given you already have NEXUS that would be moot.
I'd recommend that if possible, that each of your kids has and brings a fully charged noise cancelling headphone since airplanes are quite noisy, which along with potentially cramped seats, can pose some sensory challenges. In the event you're looking at standard economy seats, I would consider a routing that involves a 787 rather than a 737 if possible, as the former provides a better ride and, at least in my experience, is not as loud.
I hope this helps!