Occasionally, when I head back from GTA to KW, instead of going down 401, I use 403 then 24 (so via Brantford). Traffic’s somewhat heavy during rush hour between Brantford and Hamilton nowadays, where the highway only has 4 lanes.
During rush hours when 401’s helplessly congested, I’ll also use 7 via Georgetown, Acton, Rockwood and Guelph. By the time I get to Guelph, it’s late enough that traffic clears on 7 between Guelph and Kitchener. Slow drivers between Acton and Rockeood are frustrating though.
Going between London and Waterloo, I’ve also done 4 then 7/8 instead of the 401. It was the first Saturday in January 2017. I got my car in January 2016 and the first Saturday after I got it, I drove to Stratford to check it out. Basically, on the first Saturday of January 2017, I stopped by Stratford to “celebrate the anniversary of the adventure”.
As for between GTA and Ottawa, every now and then I use the 7 as well, although 6 times out of 7 I was using it to go back to GTA. Again, I really don’t like the slow drivers on that road. Also, during summer weekends, one can see cops hiding here and there.