The way I see it, I-75 breaks up nicely over 3 days, whereas from what people say I-79 is best done over two, BUT if you're leaving after work you can probably reach Pittsburgh (or at least Erie) before sleeping. I-79 seems to be the better option though, in spite of the 402-like stretches of nothing.
For I-75, you'd hit the Ambassador Bridge in about 3-4 hours, and then you'd reach Toledo, Findlay, Lima, Dayton and Cincinnati every 45 minutes or so. Probably sleeping in Windsor is your best option there - might as well not get killed by the US dollar before you have to. But if you do that, you're going to hit cross-border traffic on Friday morning, and I'm not sure you'd want that.