I live in the middle of Cleveland-Pittsburgh near Beaver, PA and although I can't tell you much about the Cleveland side of it, I may be able to help with the middle and the Pgh side of it. There's two tour books that should help greatly.
Check out a great little book 'The Cleveland / Pittsburgh Connector", dated 2001 by Anthony F. Ratajczak, ISBN 0-9716165-0-7. I bought my copy at a LBS, Snitger's Bike Shop
in Beaver PA, 724.774.5905, you can probably get one there. He's done routing work for Adventure Cycling and did a very nice job. Here's a link to the book at Adventure Cycling
COLUMBIANA - BEAVER
Ratajczak offers a two paths between Columbiana OH and Beaver PA, one hilly/quiet and the other flater/busier; I've ridden the flat-busy one and it's okay with me, but it's definitely riding with cars going fast.
One question is how to traverse the confluence of the Ohio and Beaver rivers. You'll see on a map how Beaver PA sits on on the northwest side, Rochester PA sits on the Northeast side, and Monaca PA sits on the southwest side. Ratajczak's Map7 has an inset identifying the route.
Approaching Bridgewater, use an old, small bridge to cross the Beaver River into Rochester PA. (If you go straight on 51 South you'll end up on a highway bridge, which isn't great. I don't recommend it).
In Rochester you go straight in for 3 blocks, then turn right and cross the Rochester-Monaca bridge along 18-South. This is kind of strange, but it's called either the Rochester-Monaca bridge or the Monaca-Rochester bridge, depending on who won last year's football game; they actually change the signs.
You do NOT want to take Route65 south along the east shore of the Ohio. This section of Route65 has the most accidents of any road section in Beaver County.
So you're crossing the Monaca-Rochester bridge across the Ohio River. In town, turn left on Route 51-South, and you've joined the PA State Bike Route A
I ride on Route 51 often; at times it's a 4-lane limited access road without shoulders and fast cars, but generally it's OK. I see other riders out there too.
So you persist on 51South until you get to a town called Coraopolis, when you have choices to make. This is where Ratajczak's book ends.
CORAOPOLIS - PITTSBURGH (3 options)
1. You can stay on 51South until Groveton, and join the Montour Trail, which will lead you nearly to the GAP in McKeesport. There's a few gaps uncompleted, and it's a long meander off course. I love the Montour Trail, I ride it a lot, but it's going to add a lot of miles to the route. Check out the Montour Trail Map
2. You can stay on 51South and climb several major hills to downtown Pittsburgh.
3. At the south end of Coraopolis, turn onto Neville Island, which is an ugly gritty industrial island that's perfectly flat and pretty straight. At the south end of Neville Island, exit onto Route 51South in McKees Rocks, and you'll have skipped several heartbreaking hills. This is the way I'd go, but you'll have to decide for yourself. The photo below suggests the route.
Either way, on 51 South toward Pittsburgh, you're riding in a lot of traffic. McKees Rocks is a once-bustling steel town fallen into disrepair and neglect. They're not high-crime in daylight, but I wouldn't be hanging out in Spandex too long, either. Route51 is a busy major road with no shoulder. Just north of the Fort Pitt Bridge, get on the Station Square Trail:
PDF Map Station Square Trail
If you use Mary Shaw's most excellent little book, "Linking Up: Your Traffic Free Bike Trip Between Pittsburgh and Washington, DC" ISBN 0964601486, available on Amazon, they describe paths from downtown Pittsburgh to McKeesport. There's also a PDF version of the book here: Linking Up
Page 25 of the PDF describes the Pgh-McKeesport detour.
This Pittsburgh trail system will eventually connect to the GAP, but not for a few years. It dead-ends in a railroad yard a few miles short of Sandcastle, and you don't want to be crossing the tracks down there.
So the trick is, you want to get off the trail at the last road intersection before the dead end. You won't want to have to backtrack. The trail does not go as far as the Glenwood bridge. You could exit the trail at the REI store in South Side Works. Homestead and Duquesne are places where you don't want to stray from the beaten path. Proceed via busy local roads (PA837 ?) through rundown steel towns to McKeesport and join the trail.
Local bike shops along the route are Snitger's in Beaver PA, Ambridge Bike Shop in Ambridge PA, and Coraopolis Bikes in Coraopolis PA.
In summation: I've been over most of this route, and without a doubt it's a lot of riding on busy fast streets with cars. I can't understate this: if you're not comfortable with traffic, you wouldn't want do this.
Although the view of Pittsburgh is great and I love the trail from Pgh to SouthSide, most of this ride is industrial and not pretty. After you get to the GAP, you'll be doubly grateful for a scenic no-car trail to ride.
I do recommend both Ratajczak's map book and Mary Shaw's book.
If you have any questions feel free to PM me, or use this form
to email me.