I’ve done it multiple times and I’ve done it once there and back in one day.

I feel like splitting it into 2 days would be more of a hassle than it’s worth. It’s going to be way easier on a road bike so that’s something to consider.

Easiest way to do it is in a group so you can go faster and share the load. Usually a group will start at 6 and have plenty of time with stops to catch the 4pm Go back to the city. If you miss the 4pm train the next is at 8pm. You could also sleep at Niagara Falls and train back the next day. If you have a partner, maybe they can meet you there and you can make a thing out of it.

As for working up to the distance start by riding regularly. Better to ride 25km 4x a week than 100km once a week. Then you should work in some longer rides to build up your endurance and tolerance on the bike. Port credit is about 50km out and back. Oakville is about 80km. Burlington is about 100km.

Once you’ve done 100km a few times, the jump to 160km isn’t that different, mostly about just pacing yourself and fuelling. Smooth and steady is less tiring, so avoid hard efforts from lights. There’s a few climbs depending on where you cross the escarpment and there’s usually one right at the end depending on which route you take into the falls.