Carls Jr. is actually not that bad but it depends on the sandwich and I haven't had them in Canada only the US. I had one jalepeno burger (forgot the name) in the US and was surprised how good it was but I think that's because some of their burgers are flame broiled, others are not.
Flame broiling makes a big difference, it's like OLED tv versus an LCD TV.
Canada fast food is generally crap, but looking at how fat Americans are, that's probably not the worst thing. Tim Horton's ... people lining up for cardboard tasting food and average coffee, lulz. The ice cap is decent for the price in the summer I guess.
Fat Burger is like a poor man's In N' Out Burger, but I don't think In N' Out is ever coming to Canada, they're not even nationwide in the US. They would dominate the burger market if they really wanted to.
Don't know about any of the East Coast only US chains like White Castle, never had them.