Man, I keep re-reading this post and finding I skip past a bunch...

Bikeshops, as someone else had said, are few and far between - there's definitely a few en route, though. The map I mentioned above (Golden Horseshoe) has a few stores mentioned on it, with a marker on the map - we stopped at Rebel Cycles Canada in St. Catherines, which is a nice big friendly store from that experience.

If you're coming from the OSC, I'd head south whichever way you'd prefer to the Martin Goodman trail or Lakeshore and just keep going west. Lakeshore becomes a much nicer road to ride on once you're mostly past Toronto. From Mississauga (Port Credit, etc.) onwards it's fairly decent, just haul ass on that until you get to Burlington - you take a left at (before) Joseph Brant Hospital and then follow the incarnations of Beach Blvd across the skyway path.