I dug up some old (2006) info, so not sure how accurate it's going to be, but TAFL confirms the frequency mentioned, licenced to Fleetcom:
YRT has (still operational afaik) a 900 MHz LTR system with a single channel broadcased from Tangreen. The frequency is 936.575MHz and if you're trunking the system, the LCN is LCN01
YRT/Viva has partnered with York Regional Police as one of the user groups for the new police radio system. The system offers expanded and more reliable radio communications throughout the Region, City of Toronto and within the new subway lines. The system will be implemented between Q3 2013 - Q3 2014 within the Enforcement and Security group. As the system is field tested and accepted it will be expanded to other working sections within transit.
I don't know about the buses but I saw YRT security with iden type radios with keypad, not sure about YRT/VIVA buses, The buses coming out of Brampton into the York U seem to be on the Brampton LTR system but not York I don't think.