You are going to have to repeat, many times, that your baby is ticketed and you're bringing the car seat on board. That will be strange to them and they will likely try to get you to check it.
I've had to take the babe out of the carrier most times to go through security, but it seems to vary by airport and staff that day.
I used to live in south Florida - there is no direct way to get from there to Western Canada, that I'm aware of, and you're very likely to have to route through Toronto or some other large centre in the US -- like Edmonton-Denver or Edmonton-Dallas or something like that.
Technically if you have a car seat on board you are supposed to have the baby in the seat and buckled for take off and landing. That makes nursing during those times difficult.
A change of clothes for YOU, or at least a fresh shirt, will be handy.
Dress strategically if you're nursing - layers so you can be comfortable with a sleeping baby on you for a long time.
There will be a fold down tiny change table in the bathrooms on the planes as they're large enough (at least on the Toronto-Edmonton part).
Sorry for your loss...I hope your trip goes smoothly.