Well Hurontario is also the spine of Mississauga and Brampton's transit network. So it's a little different. But I'll concede those estimated levels of ridership are similar.
A while ago someone else and I (I forget off the top of my head who it was) did some number crunching on the pphpd of the Woodroffe bus lanes. It came out to between 3,500 pphpd and 4,000 pphpd. These bus lanes function very well, and there is little to no evidence of bunching or delays.
I just looked in the "Technology Choice Report" for the Ottawa LRT project, and they have the projected demands by 2031, and it's at around 4,500 pphpd for the section from Baseline to Knoxdale. If you look at the TMP for the 2031 timeframe, this section is still listed as BRT. It isn't until after the 2031 timeframe the "long-term plan" that it gets upgraded to LRT. The report is available here:
http://www.ottawa.ca/calendar/ottawa/citycouncil/tc/2009/10-21/Delcan - Rail System Study.pdf
There is no single point where BRT stops becoming viable and LRT starts becoming viable. There's an overlap of a few thousand pphpd. It's interesting how different cities define this border differently though. In the report that I mentioned above, they put the threshold of BRT to LRT at around 8,000 pphpd (page 11).
Personally, for at-grade options, I see BRT being useful from between 1,500 pphpd to about 5,500 pphpd (depending on operating environment obviously, I'm assuming the case of a typical suburban arterial). LRT for the same scenario I see being effective from about 4,000 pphpd to about 10,000 pphpd. Grade-separated BRT is effective from about 3,000 pphpd to around 10,000 pphpd, with grade-separated LRT being effective from 8,000 pphpd to about 20,000 pphpd. It's when a line's projected capacity falls within these grey areas that debate can ensue over which technology choice is more appropriate.