Doesn't matter, particuarly for Ottawa, Kitchener and Hamilton - and conversion isn't tough. It wasn't a big deal when Toronto purchased PCCs from elsewhere or sold PCCs to Alexandria, Kenosha, or various transit musems (HCRY excepted) or even leased PCCs to San Francisco or CLRVs to Boston.
I'd only suggest that Dundas and Hurontario consider using TTC gauge, but even then, I don't see the need. Theoretically, even the TC lines could be standard gauge!
And what if Ottawa's LRT ends up crossing the Ottawa River? Would we then see Quebec stuck with Anglo-Canadian track gauges?