So the idea was, since you can (by doing three sides of the curvy square) go from Guildwood GO station to Rouge Hill GO station entirely on a (lovely, paved) trail, to see if the upper part of the trail was as pleasant as the lower part of the trail.
Which meant getting to Guildwood, and the nigh-traditional Exhibition Station start.
The entire park was gorgeous; there's a variety of habitat, some considerable stretches identified as good for mourning warblers (which were heard, by those with suitable ears, but not seen), and if it rained it did not do so very thoroughly until we were quite out of the park. Twelve kilometers is fairly long for a bird walk, but not fatally so. And even on bicycles, it was a very pleasant, quiet, full-of-spring-and-birdsong thing.
It was a nice ride, if a bit (40km) short, and I have put walking the route (or, rather, the part of it between Guildwood and Rouge Hill) on my calendar for next spring around peak warbler season.