Has anyone biked the Cataraqui trail? It apparently goes from Smith Falls all the way to near Napanee, and I am wondering if it would be a good route to take if I were to bike from Ottawa to Toronto with a loaded touring bike (albeit with big fat tires).

I've never heard anyone even mention it, and once I was in Smith Falls and asked about it and no one even knew of it... I thought maybe it's more of a hiking or winter trail.

What about the Waterfront trail? Is that a real trail, or just suggested quiet roads?

I've never heard of that trail, would you have some more info?
I can offer this alternative, if you're interested https://www.hedney.com/ottawa.htm The route doesn't really follow either trail, but I've ridden bits of his various suggested routes, and have been always very happy with them.
Also, few years ago I rode from Kingston to Cornwall along the St Lawrence River and it's really gorgeous there.

I did more research on the Cataraqui and found this discussion, which seems to confirm my impression that it's not terribly geared towards touring cyclists, more for mountain bikers and ATVers looking for lots of mud and flies...

It's certainly harder to find reliable detailed info about bike touring than it is in Quebec. It seems like Prince Edward county is a good place to bike though, so that might be a good detour on the way to TO via the elusive Waterfront trail.

The Waterfront trail is mostly quiet roads and is quite nice.

Thanks for your research, that's good to know.

Prince Edward County is a very nice place to ride, I'm sure you'll enjoy it. Past Kingston, you can take hwy 33 and take Glenora ferry over to PEC.
We rode from PEC to Toronto few years ago and it was very nice, but had to ride against the wind the whole way :-/

Here's the official trail site: https://www.cataraquitrail.ca/

I had not heard of this trail before, and it's on my to-do list now. I wonder what the quality of the surface is compared to the Kingston-Pembroke trail, which I've ridden many times.

OK so in 2010 I rode or tried to ride the Cataraqui Trail from Strafcona to Smith Falls with my Cannondale touring bike loaded with my panniers. There was only one section where I was able to ride without fear of breaking something. For the most part the trail is too rough or unridable at all for anything but a mountain or comfort bike. If I was going to ride it again loaded I would use my mountain bike with a trailer. On this trip I ended up using paved roads that follow the trail. With the right bike it would be a wonderful trip with lots of nice spots along the trail to camp with beautiful vistas and some very nice side trips along the Rideau canal system. Didn't know till this trip that you can camp at a lock for $4.90, no shower but washrooms and of course lots of places to swim. Chaffeys Lock was my favorite.