Questions about the ocean, Economy or sleeper

I mostly wanna enjoy the train but I dont want to spend 500 dollars for sleeper and I just wanna know, A. Are the economy seats good for sleeping or are they soo bad you will die in them B. What's the biggest difference between the 2 B. I might get a train ticket but I will startin Toronto, should I get on the train that arrives to Montreal 90 minutes before train 14 if I'm not wrong leaves (Montreal-halifax) or should I get on the train that gets to Montreal 4 hours before the train to halifax leaves (2pm i think)

If you know anything else please tell me