Below is a post about diapers that says espite the same brand,the products are different:

Came from Alexandia at this thread at n.com:
http://www.negril.com/discus/messages/83412/90964.html

"Also, bring your own diapers and wipes. I ran out while there and it was awful! The diapers are crazy expensive, and while they do have Huggies (the brand I use) they were NOTHING like the Huggies at home. They were thin and hard as cardboard and leaked like you couldn't imagine! Wipes were thin and barely wet enough to wipe a bottom with!
If he's on formula, I suggest you bring that too... expensive, and sometimes they are out of your brand! Hope this helps!"

I would say 4 months would be easier. AND pack your bouncy chair! I brought my daughter down at 6 weeks and her bouncy chair came apart, so I put the legs and everything in the suitcase first, and then packed everything else on top. Also, check with AirCanada's rules, but most airlines don't penalize you for a carseat. It shouldn' count against the number of bags you check. I always bring two suitcases and a carseat, and don't get charged, because you are allowed to bring child items for free. But check with AirCanada, as I have never flown with them before.
However, when my daughter was 6 weeks old, we had a stroller that the carseat connected to (Graco) so I brought the whole contraption right up to the gate with me, and then left it at the door and they put it under and I got it when we landed.

Also, bring your own diapers and wipes. I ran out while there and it was awful! The diapers are crazy expensive, and while they do have Huggies (the brand I use) they were NOTHING like the Huggies at home. They were thin and hard as cardboard and leaked like you couldn't imagine! Wipes were thin and barely wet enough to wipe a bottom with!
If he's on formula, I suggest you bring that too... expensive, and sometimes they are out of your brand! Hope this helps!